diff --git a/app/services/ci/runners/assign_runner_service.rb b/app/services/ci/runners/assign_runner_service.rb
index 0e16ac352316590e3d795a58e329f0c6ff26402b..886cd3a4e44120c0222f65f4e87b103679a4ccf3 100644
--- a/app/services/ci/runners/assign_runner_service.rb
+++ b/app/services/ci/runners/assign_runner_service.rb
@@ -3,9 +3,9 @@
 module Ci
   module Runners
     class AssignRunnerService
-      # @param [Ci::Runner] runner the runner to assign to a project
-      # @param [Project] project the new project to assign the runner to
-      # @param [User] user the user performing the operation
+      # @param [Ci::Runner] runner: the runner to assign to a project
+      # @param [Project] project: the new project to assign the runner to
+      # @param [User] user: the user performing the operation
       def initialize(runner, project, user)
         @runner = runner
         @project = project
@@ -17,6 +17,12 @@ def execute
 
         @runner.assign_to(@project, @user)
       end
+
+      private
+
+      attr_reader :runner, :project, :user
     end
   end
 end
+
+Ci::Runners::AssignRunnerService.prepend_mod
diff --git a/ee/app/services/audit_events/runner_audit_event_service.rb b/ee/app/services/audit_events/runner_audit_event_service.rb
index b913202e38dfe0e4c9a296c1003d8c1fd1ff9dc9..84d749b9560c3e9e26b3ea14ee86bdf5620dae77 100644
--- a/ee/app/services/audit_events/runner_audit_event_service.rb
+++ b/ee/app/services/audit_events/runner_audit_event_service.rb
@@ -19,6 +19,7 @@ def initialize(runner, author, token_scope)
         target_type: runner.class.name,
         target_details: runner_path
       }
+      details.merge!(entity_id: @token_scope.id, entity_type: @token_scope.class.name) if @token_scope
 
       if author.is_a?(String)
         author = author[0...8]
diff --git a/ee/app/services/audit_events/runner_custom_audit_event_service.rb b/ee/app/services/audit_events/runner_custom_audit_event_service.rb
new file mode 100644
index 0000000000000000000000000000000000000000..d3f86e9358e5e528428ce9582c202f11d85a9b00
--- /dev/null
+++ b/ee/app/services/audit_events/runner_custom_audit_event_service.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module AuditEvents
+  class RunnerCustomAuditEventService < RunnerAuditEventService
+    # Logs an audit event with a custom message related to a runner event
+    #
+    # @param [Ci::Runner] runner
+    # @param [String, User] author: the entity initiating the operation (e.g. a runner registration or authentication token)
+    # @param [Group, Project, nil] token_scope: the scopes that the operation applies to (nil represents the instance)
+    # @param [String] custom_message: the message describing the event
+    def initialize(runner, author, token_scope, custom_message)
+      @custom_message = custom_message
+
+      super(runner, author, token_scope)
+    end
+
+    def message
+      @custom_message
+    end
+  end
+end
diff --git a/ee/app/services/ee/ci/runners/assign_runner_service.rb b/ee/app/services/ee/ci/runners/assign_runner_service.rb
new file mode 100644
index 0000000000000000000000000000000000000000..085ffc13cc1a504f404bebd4f1492397cc778f24
--- /dev/null
+++ b/ee/app/services/ee/ci/runners/assign_runner_service.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module EE
+  module Ci
+    module Runners
+      module AssignRunnerService
+        extend ::Gitlab::Utils::Override
+        include ::Audit::Changes
+
+        override :execute
+        def execute
+          result = super
+
+          audit_log_event if result
+
+          result
+        end
+
+        private
+
+        AUDIT_MESSAGE = 'Assigned CI runner to project'
+
+        def audit_log_event
+          ::AuditEvents::RunnerCustomAuditEventService.new(runner, user, project, AUDIT_MESSAGE).track_event
+        end
+      end
+    end
+  end
+end
diff --git a/ee/spec/services/audit_events/register_runner_audit_event_service_spec.rb b/ee/spec/services/audit_events/register_runner_audit_event_service_spec.rb
index 7c49a9b1040cda06f09c8c166c0c36a1f455ee78..97fd0f2d85870af56731950a54b86af49e58f1d2 100644
--- a/ee/spec/services/audit_events/register_runner_audit_event_service_spec.rb
+++ b/ee/spec/services/audit_events/register_runner_audit_event_service_spec.rb
@@ -116,6 +116,8 @@
             author_name: author[0...8],
             runner_registration_token: author[0...8],
             custom_message: 'Registered group CI runner',
+            entity_id: entity.id,
+            entity_type: entity.class.name,
             entity_path: entity.full_path,
             target_details: target_details
           }
@@ -173,6 +175,8 @@
             details: {
               author_name: author[0...8],
               runner_registration_token: author[0...8],
+              entity_id: entity.id,
+              entity_type: entity.class.name,
               entity_path: entity.full_path,
               target_details: target_details
             }
diff --git a/ee/spec/services/audit_events/runner_custom_audit_event_service_spec.rb b/ee/spec/services/audit_events/runner_custom_audit_event_service_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..db3422021c6308a6908e8898aab052ee211a65d5
--- /dev/null
+++ b/ee/spec/services/audit_events/runner_custom_audit_event_service_spec.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe AuditEvents::RunnerCustomAuditEventService do
+  describe '#security_event' do
+    let(:logger) { instance_double(Gitlab::AuditJsonLogger) }
+
+    let(:user) { create(:user) }
+    let(:entity) { create(:project) }
+    let(:target_details) { ::Gitlab::Routing.url_helpers.project_runner_path(entity, runner) }
+    let(:target_id) { runner.id }
+    let(:target_type) { 'Ci::Runner' }
+    let(:entity_type) { 'Project' }
+    let(:runner) { create(:ci_runner, :project, projects: [entity]) }
+    let(:custom_message) { 'Custom Event' }
+    let(:service) { described_class.new(runner, user, entity, custom_message) }
+
+    before do
+      stub_licensed_features(audit_events: true)
+    end
+
+    it 'logs the event to file' do
+      expect(service).to receive(:file_logger).and_return(logger)
+      expect(logger).to receive(:info).with(author_id: user.id,
+                                            author_name: user.name,
+                                            entity_id: entity.id,
+                                            entity_type: entity_type,
+                                            custom_message: custom_message,
+                                            target_details: target_details,
+                                            target_id: target_id,
+                                            target_type: target_type)
+
+      expect { service.security_event }.to change(AuditEvent, :count).by(1)
+
+      security_event = AuditEvent.last
+
+      expect(security_event.details).to eq(
+        author_name: user.name,
+        custom_message: custom_message,
+        entity_id: entity.id,
+        entity_type: entity_type,
+        target_details: target_details,
+        target_id: target_id,
+        target_type: target_type
+      )
+
+      expect(security_event.author_id).to eq(user.id)
+      expect(security_event.entity_id).to eq(entity.id)
+      expect(security_event.entity_type).to eq(entity_type)
+    end
+  end
+end
diff --git a/ee/spec/services/audit_events/unregister_runner_audit_event_service_spec.rb b/ee/spec/services/audit_events/unregister_runner_audit_event_service_spec.rb
index 5ba80eb366c10e8cc8d85e3fab18289fadad904c..d58667d5055f85480014e6fd93a9f41f9ec5fe52 100644
--- a/ee/spec/services/audit_events/unregister_runner_audit_event_service_spec.rb
+++ b/ee/spec/services/audit_events/unregister_runner_audit_event_service_spec.rb
@@ -42,6 +42,8 @@
         target_details: target_details,
         details: {
           custom_message: "Unregistered #{entity_class_name&.downcase || 'instance'} CI runner",
+          entity_id: entity&.id || -1,
+          entity_type: entity ? entity_class_name : 'User',
           entity_path: entity&.full_path,
           target_details: target_details
         }
diff --git a/ee/spec/services/ci/runners/assign_runner_service_spec.rb b/ee/spec/services/ci/runners/assign_runner_service_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..269914995864096d1d355e77fcbbfc484cacf602
--- /dev/null
+++ b/ee/spec/services/ci/runners/assign_runner_service_spec.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ::Ci::Runners::AssignRunnerService, '#execute' do
+  let_it_be(:owner_project) { create(:project) }
+  let_it_be(:new_project) { create(:project) }
+  let_it_be(:project_runner) { create(:ci_runner, :project, projects: [owner_project]) }
+
+  let(:audit_service) { instance_double(::AuditEvents::RunnerCustomAuditEventService) }
+
+  subject { described_class.new(project_runner, new_project, user).execute }
+
+  context 'with unauthorized user' do
+    let(:user) { build(:user) }
+
+    it 'does not call assign_to on runner and returns false', :aggregate_failures do
+      expect(project_runner).not_to receive(:assign_to)
+      expect(::AuditEvents::RunnerCustomAuditEventService).not_to receive(:new)
+
+      is_expected.to be_falsey
+    end
+  end
+
+  context 'with admin user', :enable_admin_mode do
+    let(:user) { create_default(:admin) }
+
+    before do
+      expect(audit_service).to receive(:track_event).once.and_return('track_event_return_value')
+    end
+
+    it 'calls track_event on RunnerCustomAuditEventService and returns assign_to return value', :aggregate_failures do
+      expect(project_runner).to receive(:assign_to).with(new_project, user).once.and_return('assign_to return value')
+      expect(::AuditEvents::RunnerCustomAuditEventService).to receive(:new)
+        .with(project_runner, user, new_project, 'Assigned CI runner to project')
+        .once.and_return(audit_service)
+
+      is_expected.to eq('assign_to return value')
+    end
+  end
+end
diff --git a/spec/services/ci/runners/assign_runner_service_spec.rb b/spec/services/ci/runners/assign_runner_service_spec.rb
index 2997dfd702798996c04851cd057de78bc270d2d2..00b176bb759ec5b3f1d53435ee2130c964fe9b00 100644
--- a/spec/services/ci/runners/assign_runner_service_spec.rb
+++ b/spec/services/ci/runners/assign_runner_service_spec.rb
@@ -5,8 +5,8 @@
 RSpec.describe ::Ci::Runners::AssignRunnerService, '#execute' do
   subject { described_class.new(runner, project, user).execute }
 
-  let_it_be(:runner) { build(:ci_runner) }
-  let_it_be(:project) { build(:project) }
+  let_it_be(:runner) { create(:ci_runner, :project, projects: [project]) }
+  let_it_be(:project) { create(:project) }
 
   context 'without user' do
     let(:user) { nil }