diff --git a/db/post_migrate/20251215020858_sync_bigint_foreign_keys_validation_on_merge_requests_stage_two.rb b/db/post_migrate/20251215020858_sync_bigint_foreign_keys_validation_on_merge_requests_stage_two.rb
new file mode 100644
index 0000000000000000000000000000000000000000..60256ec679b7dccd9039f03b6585adc792748916
--- /dev/null
+++ b/db/post_migrate/20251215020858_sync_bigint_foreign_keys_validation_on_merge_requests_stage_two.rb
@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+class SyncBigintForeignKeysValidationOnMergeRequestsStageTwo < Gitlab::Database::Migration[2.3]
+  include Gitlab::Database::PartitioningMigrationHelpers::ForeignKeyHelpers
+
+  disable_ddl_transaction!
+  milestone '18.8'
+
+  TABLE_NAME = 'merge_requests'
+  COLUMNS = %i[target_project_id latest_merge_request_diff_id last_edited_by_id].freeze
+  FOREIGN_KEYS = [
+    {
+      source_table: :merge_requests,
+      column: :target_project_id_convert_to_bigint,
+      name: :fk_a6963e8447
+    },
+    {
+      source_table: :merge_requests,
+      column: :latest_merge_request_diff_id_convert_to_bigint,
+      name: :fk_06067f5644
+    }
+  ].freeze
+  PARTITIONED_FOREIGN_KEYS = [
+    {
+      source_table: :p_generated_ref_commits,
+      column: [:project_id, :merge_request_iid],
+      target_table: :merge_requests,
+      target_column: [:target_project_id_convert_to_bigint, :iid],
+      on_delete: :cascade,
+      name: :fk_generated_ref_commits_merge_request_id,
+      reverse_lock_order: true
+    }
+  ].freeze
+
+  def up
+    conversion_needed = COLUMNS.all? do |column|
+      column_exists?(TABLE_NAME, convert_to_bigint_column(column))
+    end
+
+    unless conversion_needed
+      say "No conversion columns found - no need to create bigint FKs"
+      return
+    end
+
+    # synchronously validates un-partitioned FKs
+    FOREIGN_KEYS.each do |fk|
+      validate_foreign_key fk[:source_table], fk[:column], name: tmp_name(fk[:name])
+    end
+
+    # synchronously validates partitioned FKs
+    PARTITIONED_FOREIGN_KEYS.each do |fk|
+      add_concurrent_partitioned_foreign_key(
+        fk[:source_table],
+        fk[:target_table],
+        column: fk[:column],
+        target_column: fk[:target_column],
+        name: tmp_name(fk[:name]),
+        on_delete: fk[:on_delete],
+        validate: true,
+        reverse_lock_order: fk[:reverse_lock_order]
+      )
+    end
+  end
+
+  def down
+    # no-op
+  end
+
+  private
+
+  def tmp_name(name)
+    "#{name}_tmp"
+  end
+end
diff --git a/db/post_migrate/20251215020900_swap_columns_for_merge_requests_bigint_conversion_stage_two.rb b/db/post_migrate/20251215020900_swap_columns_for_merge_requests_bigint_conversion_stage_two.rb
new file mode 100644
index 0000000000000000000000000000000000000000..ba97e82ba9acd4a4a94cd6cc193123ffa23bd05e
--- /dev/null
+++ b/db/post_migrate/20251215020900_swap_columns_for_merge_requests_bigint_conversion_stage_two.rb
@@ -0,0 +1,117 @@
+# frozen_string_literal: true
+
+class SwapColumnsForMergeRequestsBigintConversionStageTwo < Gitlab::Database::Migration[2.3]
+  include Gitlab::Database::MigrationHelpers::Swapping
+  include Gitlab::Database::MigrationHelpers::ConvertToBigint
+  include Gitlab::Database::MigrationHelpers::WraparoundAutovacuum
+  include Gitlab::Database::PartitioningMigrationHelpers::ForeignKeyHelpers
+  include Gitlab::Database::PartitioningMigrationHelpers::IndexHelpers
+
+  disable_ddl_transaction!
+  milestone '18.8'
+
+  TABLE_NAME = 'merge_requests'
+  COLUMNS = %w[target_project_id latest_merge_request_diff_id last_edited_by_id].freeze
+
+  INDEXES = %w[
+    index_merge_requests_on_target_project_id_and_iid
+    index_merge_requests_on_target_project_id_and_merged_commit_sha
+    index_merge_requests_on_target_project_id_and_source_branch
+    index_merge_requests_on_target_project_id_and_squash_commit_sha
+    index_merge_requests_on_target_project_id_and_target_branch
+    index_merge_requests_for_latest_diffs_with_state_merged
+    index_merge_requests_on_latest_merge_request_diff_id
+    idx_mrs_on_target_id_and_created_at_and_state_id
+    index_merge_requests_on_target_project_id_and_created_at_and_id
+    index_merge_requests_on_target_project_id_and_updated_at_and_id
+    index_merge_requests_on_tp_id_and_merge_commit_sha_and_id
+    index_merge_requests_on_author_id_and_target_project_id
+    index_on_merge_requests_for_latest_diffs
+  ].freeze
+
+  FOREIGN_KEYS = [
+    {
+      table_name: TABLE_NAME,
+      fk_name: 'fk_a6963e8447'
+    },
+    {
+      table_name: TABLE_NAME,
+      fk_name: 'fk_06067f5644'
+    }
+  ]
+  PARTITIONED_FOREIGN_KEYS = [
+    {
+      table_name: 'p_generated_ref_commits',
+      fk_name: 'fk_generated_ref_commits_merge_request_id'
+    }
+  ].freeze
+
+  def up
+    return if skip_migration_as_bigint_columns_non_exist || skip_migration_as_bigint_columns_type_non_match('bigint')
+
+    swap
+  end
+
+  def down
+    return if skip_migration_as_bigint_columns_non_exist || skip_migration_as_bigint_columns_type_non_match('integer')
+
+    swap
+  end
+
+  private
+
+  def swap
+    unless can_execute_on?(:merge_requests)
+      raise StandardError,
+        "Wraparound prevention vacuum detected on merge_requests table" \
+          "Please try again later."
+    end
+
+    # rubocop:disable Migration/WithLockRetriesDisallowedMethod -- custom implementation
+    with_lock_retries(raise_on_exhaustion: true) do
+      COLUMNS.each do |column|
+        swap_columns(TABLE_NAME, column, convert_to_bigint_column(column))
+      end
+
+      reset_all_trigger_functions(TABLE_NAME)
+
+      INDEXES.each do |index|
+        bigint_idx_name = bigint_index_name(index)
+        swap_indexes(TABLE_NAME, index, bigint_idx_name)
+      end
+
+      FOREIGN_KEYS.each do |foreign_key|
+        bigint_fk_temp_name = tmp_name(foreign_key[:fk_name])
+        swap_foreign_keys(foreign_key[:table_name], foreign_key[:fk_name], bigint_fk_temp_name)
+      end
+
+      PARTITIONED_FOREIGN_KEYS.each do |foreign_key|
+        bigint_fk_temp_name = tmp_name(foreign_key[:fk_name])
+        swap_partitioned_foreign_keys(foreign_key[:table_name], foreign_key[:fk_name], bigint_fk_temp_name)
+      end
+    end
+    # rubocop:enable Migration/WithLockRetriesDisallowedMethod
+  end
+
+  def tmp_name(name)
+    "#{name}_tmp"
+  end
+
+  def skip_migration_as_bigint_columns_non_exist
+    unless COLUMNS.all? { |column| column_exists?(TABLE_NAME, convert_to_bigint_column(column)) }
+      say "No conversion columns found - migration skipped"
+      return true
+    end
+
+    false
+  end
+
+  def skip_migration_as_bigint_columns_type_non_match(column_type)
+    unless COLUMNS.all? { |column| column_for(TABLE_NAME, convert_to_bigint_column(column)).sql_type == column_type }
+      say "Columns are converted - migration skipped"
+      return true
+    end
+
+    false
+  end
+end
diff --git a/db/post_migrate/20251215020901_drop_tmp_bigint_indexes_and_fks_on_merge_requests_stage_two.rb b/db/post_migrate/20251215020901_drop_tmp_bigint_indexes_and_fks_on_merge_requests_stage_two.rb
new file mode 100644
index 0000000000000000000000000000000000000000..59a81c8ab233af7520789d0aff11be89878fca97
--- /dev/null
+++ b/db/post_migrate/20251215020901_drop_tmp_bigint_indexes_and_fks_on_merge_requests_stage_two.rb
@@ -0,0 +1,203 @@
+# frozen_string_literal: true
+
+class DropTmpBigintIndexesAndFksOnMergeRequestsStageTwo < Gitlab::Database::Migration[2.3]
+  include Gitlab::Database::MigrationHelpers::ConvertToBigint
+  include Gitlab::Database::MigrationHelpers::WraparoundAutovacuum
+  include Gitlab::Database::PartitioningMigrationHelpers::ForeignKeyHelpers
+
+  disable_ddl_transaction!
+  milestone '18.8'
+
+  TABLE_NAME = 'merge_requests'
+  COLUMNS = %w[target_project_id latest_merge_request_diff_id last_edited_by_id].freeze
+
+  INDEXES = [
+    {
+      name: 'index_merge_requests_on_target_project_id_and_iid',
+      columns: [:target_project_id_convert_to_bigint, :iid],
+      options: { unique: true }
+    },
+    {
+      name: 'index_merge_requests_on_target_project_id_and_merged_commit_sha',
+      columns: [:target_project_id_convert_to_bigint, :merged_commit_sha]
+    },
+    {
+      name: 'index_merge_requests_on_target_project_id_and_source_branch',
+      columns: [:target_project_id_convert_to_bigint, :source_branch]
+    },
+    {
+      name: 'index_merge_requests_on_target_project_id_and_squash_commit_sha',
+      columns: [:target_project_id_convert_to_bigint, :squash_commit_sha]
+    },
+    {
+      name: 'index_merge_requests_on_target_project_id_and_target_branch',
+      columns: [:target_project_id_convert_to_bigint, :target_branch],
+      options: { where: "state_id = 1 AND merge_when_pipeline_succeeds = true" }
+    },
+    {
+      name: 'index_merge_requests_for_latest_diffs_with_state_merged',
+      columns: [:latest_merge_request_diff_id_convert_to_bigint, :target_project_id_convert_to_bigint],
+      options: { where: "state_id = 3" }
+    },
+    {
+      name: 'index_merge_requests_on_latest_merge_request_diff_id',
+      columns: [:latest_merge_request_diff_id_convert_to_bigint]
+    },
+    {
+      name: 'idx_mrs_on_target_id_and_created_at_and_state_id',
+      columns: [:target_project_id_convert_to_bigint, :state_id, :created_at, :id]
+    },
+    {
+      name: 'index_merge_requests_on_target_project_id_and_created_at_and_id',
+      columns: [:target_project_id_convert_to_bigint, :created_at, :id]
+    },
+    {
+      name: 'index_merge_requests_on_target_project_id_and_updated_at_and_id',
+      columns: [:target_project_id_convert_to_bigint, :updated_at, :id]
+    },
+    {
+      name: 'index_merge_requests_on_tp_id_and_merge_commit_sha_and_id',
+      columns: [:target_project_id_convert_to_bigint, :merge_commit_sha, :id]
+    },
+    {
+      name: 'index_merge_requests_on_author_id_and_target_project_id',
+      columns: [:author_id, :target_project_id_convert_to_bigint]
+    },
+    {
+      name: 'index_on_merge_requests_for_latest_diffs',
+      columns: [:target_project_id_convert_to_bigint],
+      options: { include: [:id, :latest_merge_request_diff_id_convert_to_bigint] }
+    }
+  ].freeze
+
+  FOREIGN_KEYS = [
+    {
+      source_table: :merge_requests,
+      column: :target_project_id_convert_to_bigint,
+      target_table: :projects,
+      target_column: :id,
+      on_delete: :cascade,
+      name: :fk_a6963e8447,
+      reverse_lock_order: true
+    },
+    {
+      source_table: :merge_requests,
+      column: :latest_merge_request_diff_id_convert_to_bigint,
+      target_table: :merge_request_diffs,
+      target_column: :id,
+      on_delete: :nullify,
+      name: :fk_06067f5644,
+      reverse_lock_order: false
+    }
+  ].freeze
+  PARTITIONED_FOREIGN_KEYS = [
+    {
+      source_table: :p_generated_ref_commits,
+      column: [:project_id, :merge_request_iid],
+      target_table: :merge_requests,
+      target_column: [:target_project_id_convert_to_bigint, :iid],
+      on_delete: :cascade,
+      name: :fk_generated_ref_commits_merge_request_id,
+      reverse_lock_order: true
+    }
+  ].freeze
+
+  def up
+    vacuum_detection
+    return if skip_migration_as_bigint_columns_non_exist || skip_migration_as_bigint_columns_type_non_match('integer')
+
+    # rubocop:disable Migration/WithLockRetriesDisallowedMethod -- custom implementation
+    with_lock_retries(raise_on_exhaustion: true) do
+      FOREIGN_KEYS.each do |foreign_key|
+        remove_foreign_key_if_exists(
+          foreign_key[:source_table],
+          foreign_key[:target_table],
+          name: tmp_name(foreign_key[:name]),
+          reverse_lock_order: foreign_key[:reverse_lock_order]
+        )
+      end
+    end
+    # rubocop:enable Migration/WithLockRetriesDisallowedMethod
+
+    PARTITIONED_FOREIGN_KEYS.each do |foreign_key|
+      remove_partitioned_foreign_key(
+        foreign_key[:source_table],
+        foreign_key[:target_table],
+        name: tmp_name(foreign_key[:name]),
+        reverse_lock_order: foreign_key[:reverse_lock_order]
+      )
+    end
+
+    INDEXES.each do |index|
+      remove_concurrent_index_by_name(TABLE_NAME, bigint_index_name(index[:name]))
+    end
+  end
+
+  def down
+    vacuum_detection
+    return if skip_migration_as_bigint_columns_non_exist || skip_migration_as_bigint_columns_type_non_match('integer')
+
+    INDEXES.each do |index|
+      options = index[:options] || {}
+      add_concurrent_index TABLE_NAME, index[:columns], name: bigint_index_name(index[:name]), **options
+    end
+
+    FOREIGN_KEYS.each do |foreign_key|
+      add_concurrent_foreign_key(
+        foreign_key[:source_table],
+        foreign_key[:target_table],
+        column: foreign_key[:column],
+        target_column: foreign_key[:target_column],
+        name: tmp_name(fforeign_keyk[:name]),
+        on_delete: foreign_key[:on_delete],
+        validate: true,
+        reverse_lock_order: foreign_key[:reverse_lock_order]
+      )
+    end
+
+    PARTITIONED_FOREIGN_KEYS.each do |fk|
+      add_concurrent_partitioned_foreign_key(
+        fk[:source_table],
+        fk[:target_table],
+        column: fk[:column],
+        target_column: fk[:target_column],
+        name: tmp_name(fk[:name]),
+        on_delete: fk[:on_delete],
+        validate: true,
+        reverse_lock_order: fk[:reverse_lock_order]
+      )
+    end
+  end
+
+  private
+
+  def tmp_name(name)
+    "#{name}_tmp"
+  end
+
+  def skip_migration_as_bigint_columns_non_exist
+    unless COLUMNS.all? { |column| column_exists?(TABLE_NAME, convert_to_bigint_column(column)) }
+      say "No conversion columns found - migration skipped"
+      return true
+    end
+
+    false
+  end
+
+  def skip_migration_as_bigint_columns_type_non_match(column_type)
+    unless COLUMNS.all? { |column| column_for(TABLE_NAME, convert_to_bigint_column(column)).sql_type == column_type }
+      say "Columns are converted - migration skipped"
+      return true
+    end
+
+    false
+  end
+
+  def vacuum_detection
+    return if can_execute_on?(:merge_requests)
+
+    raise StandardError,
+      "Wraparound prevention vacuum detected on merge_requests table" \
+        "Please try again later."
+  end
+end
diff --git a/db/schema_migrations/20251215020858 b/db/schema_migrations/20251215020858
new file mode 100644
index 0000000000000000000000000000000000000000..ab8ec21cdef2abd56eacfd13ad382425dea88e58
--- /dev/null
+++ b/db/schema_migrations/20251215020858
@@ -0,0 +1 @@
+4daa929f4f98ec875db23ecf8868a1da4fc8afa05d2e5509fdeb5177a1044804
\ No newline at end of file
diff --git a/db/schema_migrations/20251215020900 b/db/schema_migrations/20251215020900
new file mode 100644
index 0000000000000000000000000000000000000000..d26c9a09bbce7b393106fe8c2d31d440a0a76153
--- /dev/null
+++ b/db/schema_migrations/20251215020900
@@ -0,0 +1 @@
+e2cbe9d02332cb2d382244159fbae91c154b53254551749d4164307653b0cd86
\ No newline at end of file
diff --git a/db/schema_migrations/20251215020901 b/db/schema_migrations/20251215020901
new file mode 100644
index 0000000000000000000000000000000000000000..991999a505870eeeaf7775dbf27b857c486debc0
--- /dev/null
+++ b/db/schema_migrations/20251215020901
@@ -0,0 +1 @@
+6271539a1a34520a18a8e662467582e79d77c79bce193fe2482a608d5e22e4bc
\ No newline at end of file