diff --git a/app/models/group.rb b/app/models/group.rb
index a699a997c09d6b8e81995148c82110f20ea4e6a3..8a57c0f4177c0145bc65f02cb67bf037949b47f7 100644
--- a/app/models/group.rb
+++ b/app/models/group.rb
@@ -1293,6 +1293,26 @@ def pending_delete?
     deletion_schedule.marked_for_deletion_on.future?
   end
 
+  def unarchive_self_and_descendants!
+    NamespaceSetting
+      .where(namespace_id: self_and_descendant_ids, archived: true)
+      .update_all(archived: false)
+  end
+
+  def unarchive_descendants!
+    NamespaceSetting
+      .where(namespace_id: descendant_ids, archived: true)
+      .update_all(archived: false)
+  end
+
+  def unarchive_all_projects!
+    Project
+      .joins(:namespace)
+      .where("namespaces.traversal_ids @> '{?}'", id)
+      .where(archived: true)
+      .update_all(archived: false)
+  end
+
   private
 
   def feature_flag_enabled_for_self_or_ancestor?(feature_flag, type: :development)
diff --git a/app/models/namespaces/traversal/cached.rb b/app/models/namespaces/traversal/cached.rb
index 57bacd483067a02b57cc5531c9e04e7b724941f3..67ca51af1843d77b693bb19d51c9a6ef63d1f971 100644
--- a/app/models/namespaces/traversal/cached.rb
+++ b/app/models/namespaces/traversal/cached.rb
@@ -28,6 +28,10 @@ def self_and_descendant_ids(skope: self.class)
         )
       end
 
+      def descendant_ids(skope: self.class)
+        self_and_descendant_ids(skope:).id_not_in(id)
+      end
+
       override :all_project_ids
       def all_project_ids
         scope_with_cached_ids(
diff --git a/app/services/namespaces/groups/archive_service.rb b/app/services/namespaces/groups/archive_service.rb
index 3f051069d2bdd3f6acf9cba64b437f271f0636d6..c6512b30e66b5946a5138117002906b6c195ba2b 100644
--- a/app/services/namespaces/groups/archive_service.rb
+++ b/app/services/namespaces/groups/archive_service.rb
@@ -28,10 +28,21 @@ def execute
 
         return AlreadyArchivedError if group.archived
         return AncestorAlreadyArchivedError if group.ancestors_archived?
-        return ArchivingFailedError unless group.namespace_settings.update(archived: true)
+
+        if unarchive_descendants?
+          group.transaction do
+            group.namespace_settings.update!(archived: true)
+            group.unarchive_descendants!
+            group.unarchive_all_projects!
+          end
+        else
+          group.namespace_settings.update!(archived: true)
+        end
 
         after_archive
         ServiceResponse.success
+      rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotSaved
+        ArchivingFailedError
       end
 
       private
@@ -49,6 +60,10 @@ def unlink_project_forks
       def error_response(message)
         ServiceResponse.error(message: message)
       end
+
+      def unarchive_descendants?
+        Feature.enabled?(:cascade_unarchive_group, group, type: :gitlab_com_derisk)
+      end
     end
   end
 end
diff --git a/app/services/namespaces/groups/unarchive_service.rb b/app/services/namespaces/groups/unarchive_service.rb
index e5fe74c1d97c0635e54015280629d5370d275c99..ebea17f229a2ef6aa41e5c6097db00c6310e88b5 100644
--- a/app/services/namespaces/groups/unarchive_service.rb
+++ b/app/services/namespaces/groups/unarchive_service.rb
@@ -25,10 +25,20 @@ def execute
         return NotAuthorizedError unless can?(current_user, :archive_group, group)
         return AncestorArchivedError if group.ancestors_archived?
         return AlreadyUnarchivedError unless group.archived
-        return UnarchivingFailedError unless group.namespace_settings.update(archived: false)
+
+        if unarchive_descendants?
+          group.transaction do
+            group.unarchive_self_and_descendants!
+            group.unarchive_all_projects!
+          end
+        else
+          group.namespace_settings.update!(archived: false)
+        end
 
         after_unarchive
         ServiceResponse.success
+      rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotSaved
+        UnarchivingFailedError
       end
 
       private
@@ -41,6 +51,10 @@ def after_unarchive
       def error_response(message)
         ServiceResponse.error(message: message)
       end
+
+      def unarchive_descendants?
+        Feature.enabled?(:cascade_unarchive_group, group, type: :gitlab_com_derisk)
+      end
     end
   end
 end
diff --git a/config/feature_flags/gitlab_com_derisk/cascade_unarchive_group.yml b/config/feature_flags/gitlab_com_derisk/cascade_unarchive_group.yml
new file mode 100644
index 0000000000000000000000000000000000000000..43ccf2925d6dc11cc2dab287b1ab1986b8327bc1
--- /dev/null
+++ b/config/feature_flags/gitlab_com_derisk/cascade_unarchive_group.yml
@@ -0,0 +1,11 @@
+---
+name: cascade_unarchive_group
+description: Unarchive descendant groups and projects of a group when toggling its archive state
+feature_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/578499
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/215688
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/583415
+milestone: '18.7'
+observed: true
+group: group::organizations
+type: gitlab_com_derisk
+default_enabled: false
diff --git a/lib/api/groups.rb b/lib/api/groups.rb
index e8b0c0bdaebcb34c61e37b78f858b22d8e042580..3e650860eba4f8ec52570bcc354b4365b00a9066 100644
--- a/lib/api/groups.rb
+++ b/lib/api/groups.rb
@@ -392,7 +392,7 @@ def check_query_limit; end
 
         if response.success?
           status 200
-          present_group_details(params, group, with_projects: params[:with_projects])
+          present_group_details(params, group.reset, with_projects: params[:with_projects])
         else
           render_api_error!(response.message, 422)
         end
diff --git a/spec/models/group_spec.rb b/spec/models/group_spec.rb
index ef354fcccddc821583bf6a20eb3d9603025a2ca6..d0396310e2d2c112be0d56540cff6dc1a2ee8d15 100644
--- a/spec/models/group_spec.rb
+++ b/spec/models/group_spec.rb
@@ -865,6 +865,10 @@
       it { expect(group.descendants.to_sql).to include 'traversal_ids @>' }
     end
 
+    describe '#descendant_ids' do
+      it { expect(group.descendant_ids.to_sql).to include 'traversal_ids @>' }
+    end
+
     describe '#self_and_hierarchy' do
       it { expect(group.self_and_hierarchy.to_sql).to include 'traversal_ids @>' }
     end
@@ -4673,4 +4677,101 @@ def define_cache_expectations(cache_key)
       end
     end
   end
+
+  describe '#unarchive_self_and_descendants!' do
+    let_it_be_with_reload(:parent_group) { create(:group) }
+    let_it_be_with_reload(:group) { create(:group, :archived, parent: parent_group) }
+    let_it_be_with_reload(:subgroup) { create(:group, :archived, parent: group) }
+    let_it_be_with_reload(:sub_subgroup) { create(:group, :archived, parent: subgroup) }
+
+    it 'unarchives the group itself' do
+      group.unarchive_self_and_descendants!
+
+      expect(group.namespace_settings.reload.archived).to be(false)
+    end
+
+    it 'unarchives all descendant groups', :aggregate_failures do
+      group.unarchive_self_and_descendants!
+
+      expect(subgroup.namespace_settings.reload.archived).to be(false)
+      expect(sub_subgroup.namespace_settings.reload.archived).to be(false)
+    end
+
+    it 'does not unarchive parent groups' do
+      parent_group.namespace_settings.update!(archived: true)
+
+      group.unarchive_self_and_descendants!
+
+      expect(parent_group.namespace_settings.reload.archived).to be(true)
+    end
+
+    it 'does not affect groups that are not archived' do
+      unarchived_group = create(:group, parent: group)
+
+      expect { group.unarchive_self_and_descendants! }.not_to change {
+        unarchived_group.namespace_settings.reload.archived
+      }
+    end
+  end
+
+  describe '#unarchive_descendants!' do
+    let_it_be_with_reload(:parent_group) { create(:group) }
+    let_it_be_with_reload(:group) { create(:group, :archived, parent: parent_group) }
+    let_it_be_with_reload(:subgroup) { create(:group, :archived, parent: group) }
+    let_it_be_with_reload(:sub_subgroup) { create(:group, :archived, parent: subgroup) }
+
+    it 'does not unarchive the group itself' do
+      group.unarchive_descendants!
+
+      expect(group.namespace_settings.reload.archived).to be(true)
+    end
+
+    it 'unarchives all descendant groups', :aggregate_failures do
+      group.unarchive_descendants!
+
+      expect(subgroup.namespace_settings.reload.archived).to be(false)
+      expect(sub_subgroup.namespace_settings.reload.archived).to be(false)
+    end
+
+    it 'does not unarchive parent groups' do
+      parent_group.namespace_settings.update!(archived: true)
+
+      group.unarchive_descendants!
+
+      expect(parent_group.namespace_settings.reload.archived).to be(true)
+    end
+
+    it 'does not affect groups that are not archived' do
+      unarchived_group = create(:group, parent: group)
+
+      expect { group.unarchive_descendants! }.not_to change {
+        unarchived_group.namespace_settings.reload.archived
+      }
+    end
+  end
+
+  describe '#unarchive_all_projects!' do
+    let_it_be_with_reload(:group) { create(:group) }
+    let_it_be_with_reload(:archived_project_1) { create(:project, :archived, group: group) }
+    let_it_be_with_reload(:archived_project_2) { create(:project, :archived, group: group) }
+    let_it_be_with_reload(:non_archived_project) { create(:project, group: group) }
+
+    let_it_be_with_reload(:subgroup) { create(:group, parent: group) }
+    let_it_be_with_reload(:subgroup_archived_project) { create(:project, :archived, group: subgroup) }
+    let_it_be_with_reload(:subgroup_non_archived_project) { create(:project, group: subgroup) }
+
+    it 'unarchives all archived projects in the group', :aggregate_failures do
+      group.unarchive_all_projects!
+
+      expect(archived_project_1.reload.archived).to be(false)
+      expect(archived_project_2.reload.archived).to be(false)
+      expect(subgroup_archived_project.reload.archived).to be(false)
+    end
+
+    it 'does not affect projects that are not archived' do
+      expect { group.unarchive_all_projects! }
+        .to not_change { non_archived_project.reload.archived }
+          .and not_change { subgroup_non_archived_project.reload.archived }
+    end
+  end
 end
diff --git a/spec/models/namespaces/traversal/cached_spec.rb b/spec/models/namespaces/traversal/cached_spec.rb
index c166e9b8fe3ad9b775fd12cacf0650e5379df113..09158bf950bc993166ab6b6c064c0e9f99a99f64 100644
--- a/spec/models/namespaces/traversal/cached_spec.rb
+++ b/spec/models/namespaces/traversal/cached_spec.rb
@@ -150,6 +150,43 @@
       end
     end
 
+    describe '#descendant_ids' do
+      subject(:ids) { group.descendant_ids.pluck(:id) }
+
+      it 'returns the cached values excluding self' do
+        expect(ids).to eq(namespace_descendants.self_and_descendant_group_ids - [group.id])
+      end
+
+      context 'when the cache is outdated' do
+        it 'returns the values from the uncached descendant_ids query' do
+          namespace_descendants.update!(outdated_at: Time.current)
+
+          expect(ids.sort).to match_array([subgroup.id, subsubgroup.id])
+        end
+      end
+
+      context 'when the scope is specified' do
+        subject(:ids) { group.descendant_ids(skope: Namespace).pluck(:id) }
+
+        it 'returns the cached values excluding self' do
+          expect(ids).to eq(namespace_descendants.self_and_descendant_ids - [group.id])
+        end
+
+        context 'when the cache is outdated' do
+          it 'returns the values from the uncached descendant_ids query' do
+            namespace_descendants.update!(outdated_at: Time.current)
+
+            expect(ids.sort).to eq([
+              subgroup.id, subsubgroup.id,
+              project1.project_namespace_id,
+              project2.project_namespace_id,
+              project3.project_namespace_id
+            ])
+          end
+        end
+      end
+    end
+
     describe '#all_project_ids' do
       subject(:ids) { group.all_project_ids.pluck(:id) }
 
diff --git a/spec/services/namespaces/groups/archive_service_spec.rb b/spec/services/namespaces/groups/archive_service_spec.rb
index 0c895a7f635fe87a732ed5813a0c90b60a036e33..122d227c619ab0f2c64d2ed73e7061476891abf9 100644
--- a/spec/services/namespaces/groups/archive_service_spec.rb
+++ b/spec/services/namespaces/groups/archive_service_spec.rb
@@ -61,13 +61,50 @@
   end
 
   context 'when the group is not archived' do
+    let_it_be_with_reload(:subgroup) { create(:group, :archived, parent: group) }
+    let_it_be_with_reload(:sub_subgroup) { create(:group, :archived, parent: subgroup) }
+
+    let_it_be_with_reload(:archived_project) { create(:project, :archived, group: group) }
+    let_it_be_with_reload(:archived_subgroup_project) { create(:project, :archived, group: subgroup) }
+
     before do
       group.namespace_settings.update!(archived: false)
     end
 
+    shared_examples 'rolls back all changes on failure' do
+      it 'returns an error response' do
+        response = service_response
+        expect(response).to be_error
+        expect(response.message).to eq("Failed to archive group!")
+      end
+
+      it 'does not persist any changes' do
+        expect { service_response }
+          .to not_change { group.namespace_settings.reload.archived }
+            .and not_change { subgroup.namespace_settings.reload.archived }
+              .and not_change { archived_project.reload.archived }
+      end
+    end
+
     context 'when archiving succeeds' do
-      it 'updates the namespace_settings archived attribute' do
-        expect { service_response }.to change { group.namespace_settings.reload.archived }.from(false).to(true)
+      it 'archives the group' do
+        service_response
+
+        expect(group.namespace_settings.reload.archived).to be(true)
+      end
+
+      it 'unarchives all descendant groups', :aggregate_failures do
+        service_response
+
+        expect(subgroup.namespace_settings.reload.archived).to be(false)
+        expect(sub_subgroup.namespace_settings.reload.archived).to be(false)
+      end
+
+      it 'unarchives all projects', :aggregate_failures do
+        service_response
+
+        expect(archived_project.reload.archived).to be(false)
+        expect(archived_subgroup_project.reload.archived).to be(false)
       end
 
       it 'returns a success response with the group' do
@@ -76,10 +113,10 @@
 
       it 'publishes a GroupArchivedEvent' do
         expect { service_response }.to publish_event(Namespaces::Groups::GroupArchivedEvent)
-                                        .with(
-                                          group_id: group.id,
-                                          root_namespace_id: group.root_ancestor.id
-                                        )
+          .with(
+            group_id: group.id,
+            root_namespace_id: group.root_ancestor.id
+          )
       end
 
       it 'enqueues UnlinkProjectForksWorker' do
@@ -88,18 +125,50 @@
 
         service_response
       end
+
+      context 'when `cascade_unarchive_group` flag is disabled' do
+        before do
+          stub_feature_flags(cascade_unarchive_group: false)
+        end
+
+        it 'archives the group' do
+          service_response
+
+          expect(group.namespace_settings.reload.archived).to be(true)
+        end
+
+        it 'does not modify descendant and projects archived state' do
+          expect { service_response }
+            .to not_change { subgroup.namespace_settings.reload.archived }
+              .and not_change { sub_subgroup.namespace_settings.reload.archived }
+                .and not_change { archived_project.reload.archived }
+                  .and not_change { archived_subgroup_project.reload.archived }
+        end
+      end
     end
 
     context 'when archiving fails' do
       before do
-        allow(group.namespace_settings).to receive(:update).and_return(false)
+        allow(group.namespace_settings).to receive(:update!).and_raise(ActiveRecord::RecordInvalid)
       end
 
-      it 'returns an error response with the appropriate message' do
-        response = service_response
-        expect(response).to be_error
-        expect(response.message).to eq("Failed to archive group!")
+      it_behaves_like 'rolls back all changes on failure'
+    end
+
+    context 'when unarchiving descendants fails' do
+      before do
+        allow(group).to receive(:unarchive_descendants!).and_raise(ActiveRecord::RecordNotSaved)
       end
+
+      it_behaves_like 'rolls back all changes on failure'
+    end
+
+    context 'when unarchiving projects fails' do
+      before do
+        allow(group).to receive(:unarchive_all_projects!).and_raise(ActiveRecord::RecordNotSaved)
+      end
+
+      it_behaves_like 'rolls back all changes on failure'
     end
   end
 
diff --git a/spec/services/namespaces/groups/unarchive_service_spec.rb b/spec/services/namespaces/groups/unarchive_service_spec.rb
index a1fa8b800f63b86c986e361e5d9da8a9b51eaafb..30f130110930947f59a77a68e3eaca3757cb64d5 100644
--- a/spec/services/namespaces/groups/unarchive_service_spec.rb
+++ b/spec/services/namespaces/groups/unarchive_service_spec.rb
@@ -40,14 +40,45 @@
   end
 
   context 'when the group is archived' do
+    let_it_be_with_reload(:subgroup) { create(:group, :archived, parent: group) }
+    let_it_be_with_reload(:sub_subgroup) { create(:group, :archived, parent: subgroup) }
+
+    let_it_be_with_reload(:archived_project) { create(:project, :archived, group: group) }
+    let_it_be_with_reload(:archived_subgroup_project) { create(:project, :archived, group: subgroup) }
+
     before do
       group.namespace_settings.update!(archived: true)
     end
 
+    shared_examples 'rolls back all changes on failure' do
+      it 'returns an error response' do
+        response = service_response
+        expect(response).to be_error
+        expect(response.message).to eq("Failed to unarchive group!")
+      end
+
+      it 'does not persist any changes' do
+        expect { service_response }
+          .to not_change { group.namespace_settings.reload.archived }
+            .and not_change { subgroup.namespace_settings.reload.archived }
+              .and not_change { archived_project.reload.archived }
+      end
+    end
+
     context 'when unarchiving succeeds' do
-      it 'updates namespace_settings archived to false' do
-        expect(group.namespace_settings).to receive(:update).with(archived: false).and_return(true)
+      it 'unarchives all descendant groups', :aggregate_failures do
         service_response
+
+        expect(group.namespace_settings.reload.archived).to be(false)
+        expect(subgroup.namespace_settings.reload.archived).to be(false)
+        expect(sub_subgroup.namespace_settings.reload.archived).to be(false)
+      end
+
+      it 'unarchives all projects', :aggregate_failures do
+        service_response
+
+        expect(archived_project.reload.archived).to be(false)
+        expect(archived_subgroup_project.reload.archived).to be(false)
       end
 
       it 'returns a success response with the group' do
@@ -56,23 +87,47 @@
 
       it 'publishes a GroupArchivedEvent' do
         expect { service_response }.to publish_event(Namespaces::Groups::GroupArchivedEvent)
-                                         .with(
-                                           group_id: group.id,
-                                           root_namespace_id: group.root_ancestor.id
-                                         )
+          .with(
+            group_id: group.id,
+            root_namespace_id: group.root_ancestor.id
+          )
+      end
+
+      context 'when `cascade_unarchive_group` flag is disabled' do
+        before do
+          stub_feature_flags(cascade_unarchive_group: false)
+        end
+
+        it 'unarchives the group' do
+          service_response
+
+          expect(group.namespace_settings.reload.archived).to be(false)
+        end
+
+        it 'does not modify descendant and projects archived state' do
+          expect { service_response }
+            .to not_change { subgroup.namespace_settings.reload.archived }
+              .and not_change { sub_subgroup.namespace_settings.reload.archived }
+                .and not_change { archived_project.reload.archived }
+                  .and not_change { archived_subgroup_project.reload.archived }
+        end
       end
     end
 
     context 'when unarchiving fails' do
       before do
-        allow(group.namespace_settings).to receive(:update).with(archived: false).and_return(false)
+        allow(group).to receive(:unarchive_self_and_descendants!).and_raise(ActiveRecord::RecordNotSaved)
       end
 
-      it 'returns an error response with the appropriate message' do
-        response = service_response
-        expect(response).to be_error
-        expect(response.message).to eq("Failed to unarchive group!")
+      it_behaves_like 'rolls back all changes on failure'
+    end
+
+    context 'when unarchiving projects fails' do
+      before do
+        allow(group).to receive(:unarchive_all_projects!).and_raise(ActiveRecord::RecordNotSaved)
       end
+
+      it_behaves_like 'rolls back all changes on failure'
     end
   end
 
diff --git a/spec/support/shared_examples/namespaces/traversal_examples.rb b/spec/support/shared_examples/namespaces/traversal_examples.rb
index 2099e9f88e5b75116db05e33f0e7fce60557863b..f3a262f2f0045962813295794f4c70c52f130090 100644
--- a/spec/support/shared_examples/namespaces/traversal_examples.rb
+++ b/spec/support/shared_examples/namespaces/traversal_examples.rb
@@ -384,4 +384,17 @@
       end
     end
   end
+
+  describe '#descendant_ids' do
+    subject { group.descendant_ids.pluck(:id) }
+
+    it { is_expected.to contain_exactly(nested_group.id, deep_nested_group.id, very_deep_nested_group.id) }
+
+    it 'includes project namespaces when when scope is Namespace' do
+      expect(group.descendant_ids(skope: Namespace).pluck(:id))
+        .to contain_exactly(
+          nested_group.id, deep_nested_group.id, very_deep_nested_group.id, project_namespace.id
+        )
+    end
+  end
 end