diff --git a/db/migrate/20251013100839_add_sharding_key_to_diff_note_positions.rb b/db/migrate/20251013100839_add_sharding_key_to_diff_note_positions.rb
new file mode 100644
index 0000000000000000000000000000000000000000..81420a3e94778294f619ce1212f16d930265dd7e
--- /dev/null
+++ b/db/migrate/20251013100839_add_sharding_key_to_diff_note_positions.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class AddShardingKeyToDiffNotePositions < Gitlab::Database::Migration[2.3]
+  milestone '18.6'
+
+  def change
+    add_column :diff_note_positions, :namespace_id, :bigint
+  end
+end
diff --git a/db/migrate/20251013100914_add_sharding_key_trigger_on_diff_note_positions.rb b/db/migrate/20251013100914_add_sharding_key_trigger_on_diff_note_positions.rb
new file mode 100644
index 0000000000000000000000000000000000000000..d34077d27582437cc408993c839582b882ab0a83
--- /dev/null
+++ b/db/migrate/20251013100914_add_sharding_key_trigger_on_diff_note_positions.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+class AddShardingKeyTriggerOnDiffNotePositions < Gitlab::Database::Migration[2.3]
+  include Gitlab::Database::SchemaHelpers
+
+  FUNCTION_NAME = 'sync_sharding_key_with_notes_table'
+  TRIGGER_NAME = 'set_sharding_key_for_diff_note_positions_on_insert_and_update'
+
+  milestone '18.6'
+
+  def up
+    execute(<<~SQL)
+      CREATE OR REPLACE FUNCTION #{FUNCTION_NAME}()
+      RETURNS TRIGGER AS
+      $$
+      DECLARE
+        note_project_id BIGINT;
+        note_namespace_id BIGINT;
+      BEGIN
+        IF NEW."note_id" IS NULL OR NEW."namespace_id" IS NOT NULL THEN
+          RETURN NEW;
+        END IF;
+
+        SELECT "project_id", "namespace_id"
+        INTO note_project_id, note_namespace_id
+        FROM "notes"
+        WHERE "id" = NEW."note_id";
+
+        IF note_project_id IS NOT NULL THEN
+          SELECT "project_namespace_id" FROM "projects"
+          INTO NEW."namespace_id" WHERE "projects"."id" = note_project_id;
+        ELSE
+          NEW."namespace_id" := note_namespace_id;
+        END IF;
+
+        RETURN NEW;
+      END
+      $$ LANGUAGE PLPGSQL;
+    SQL
+
+    create_trigger(:diff_note_positions, TRIGGER_NAME, FUNCTION_NAME, fires: 'BEFORE INSERT OR UPDATE')
+  end
+
+  def down
+    drop_trigger(:diff_note_positions, TRIGGER_NAME)
+  end
+end
diff --git a/db/post_migrate/20251013100952_add_not_null_constraint_on_diff_note_positions_sharding_key.rb b/db/post_migrate/20251013100952_add_not_null_constraint_on_diff_note_positions_sharding_key.rb
new file mode 100644
index 0000000000000000000000000000000000000000..d9db9989338ff4af353505847b0363718a308647
--- /dev/null
+++ b/db/post_migrate/20251013100952_add_not_null_constraint_on_diff_note_positions_sharding_key.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class AddNotNullConstraintOnDiffNotePositionsShardingKey < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.6'
+
+  def up
+    add_not_null_constraint :diff_note_positions, :namespace_id, validate: false
+  end
+
+  def down
+    remove_not_null_constraint :diff_note_positions, :namespace_id
+  end
+end
diff --git a/db/post_migrate/20251013101021_add_sharding_key_index_on_diff_note_positions.rb b/db/post_migrate/20251013101021_add_sharding_key_index_on_diff_note_positions.rb
new file mode 100644
index 0000000000000000000000000000000000000000..aa52cd05c31b8bd8b703efe4adfef568bcccac03
--- /dev/null
+++ b/db/post_migrate/20251013101021_add_sharding_key_index_on_diff_note_positions.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class AddShardingKeyIndexOnDiffNotePositions < Gitlab::Database::Migration[2.3]
+  INDEX_NAME = 'index_diff_note_positions_on_namespace_id'
+
+  milestone '18.6'
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :diff_note_positions, :namespace_id, name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :diff_note_positions, INDEX_NAME
+  end
+end
diff --git a/db/post_migrate/20251013101048_add_diff_note_positions_namespace_id_foreign_key.rb b/db/post_migrate/20251013101048_add_diff_note_positions_namespace_id_foreign_key.rb
new file mode 100644
index 0000000000000000000000000000000000000000..ded015f9152b98fcb3c2ce953d90f929a00a5347
--- /dev/null
+++ b/db/post_migrate/20251013101048_add_diff_note_positions_namespace_id_foreign_key.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class AddDiffNotePositionsNamespaceIdForeignKey < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.6'
+
+  def up
+    add_concurrent_foreign_key :diff_note_positions,
+      :namespaces,
+      column: :namespace_id,
+      reverse_lock_order: true,
+      validate: false
+  end
+
+  def down
+    with_lock_retries do
+      remove_foreign_key_if_exists(:diff_note_positions, column: :namespace_id)
+    end
+  end
+end
diff --git a/db/schema_migrations/20251013100839 b/db/schema_migrations/20251013100839
new file mode 100644
index 0000000000000000000000000000000000000000..e4fc8f8208110e8806f9d189b5a8e62296060d56
--- /dev/null
+++ b/db/schema_migrations/20251013100839
@@ -0,0 +1 @@
+8862894c50fcb33c65e9fd7eadac929cde069a0930a6b2413d33c6f56d27ed6c
\ No newline at end of file
diff --git a/db/schema_migrations/20251013100914 b/db/schema_migrations/20251013100914
new file mode 100644
index 0000000000000000000000000000000000000000..47f1ec673ce0eabbf86de6bd5983035d660b21ca
--- /dev/null
+++ b/db/schema_migrations/20251013100914
@@ -0,0 +1 @@
+7fab7fb9f9370431b9032d9508723e9aee34aa36a1a09704250f6fd04fb14970
\ No newline at end of file
diff --git a/db/schema_migrations/20251013100952 b/db/schema_migrations/20251013100952
new file mode 100644
index 0000000000000000000000000000000000000000..0b90e3863020f3214fa36d647809de605b01cd76
--- /dev/null
+++ b/db/schema_migrations/20251013100952
@@ -0,0 +1 @@
+63528f178a1325af030cfffd987718b735be29a6b820d5b1a550dab98005c5a4
\ No newline at end of file
diff --git a/db/schema_migrations/20251013101021 b/db/schema_migrations/20251013101021
new file mode 100644
index 0000000000000000000000000000000000000000..a619c2c27d9f2375ac7d6f10ecdd3653cf2b468a
--- /dev/null
+++ b/db/schema_migrations/20251013101021
@@ -0,0 +1 @@
+144181bf75fe8246f785a0ba7e0daf6ead69fd9c68e79f7d6e6494c09bf413bf
\ No newline at end of file
diff --git a/db/schema_migrations/20251013101048 b/db/schema_migrations/20251013101048
new file mode 100644
index 0000000000000000000000000000000000000000..5bb852ed171c22c11c2a263a70fbbebf526a63cd
--- /dev/null
+++ b/db/schema_migrations/20251013101048
@@ -0,0 +1 @@
+ffaa8e5ca6823a5c152cf556fd17b6f21b3ae85dbb9d380d3978eed18a55a852
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index 64d8af58f2481beba53dfe077aa42827bfa206ed..888e298e3a720c5de5d24d1735f226d3c8483e1a 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -16171,7 +16171,8 @@ CREATE TABLE diff_note_positions (
     start_sha bytea NOT NULL,
     head_sha bytea NOT NULL,
     old_path text NOT NULL,
-    new_path text NOT NULL
+    new_path text NOT NULL,
+    namespace_id bigint
 );
 
 CREATE SEQUENCE diff_note_positions_id_seq
@@ -33216,6 +33217,9 @@ ALTER TABLE push_event_payloads
 ALTER TABLE todos
     ADD CONSTRAINT check_3c13ed1c7a CHECK ((num_nonnulls(group_id, organization_id, project_id) = 1)) NOT VALID;
 
+ALTER TABLE diff_note_positions
+    ADD CONSTRAINT check_4c86140f48 CHECK ((namespace_id IS NOT NULL)) NOT VALID;
+
 ALTER TABLE ONLY instance_type_ci_runners
     ADD CONSTRAINT check_5c34a3c1db UNIQUE (id);
 
@@ -39711,6 +39715,8 @@ CREATE UNIQUE INDEX index_design_user_mentions_on_note_id ON design_user_mention
 
 CREATE INDEX index_designated_beneficiaries_on_user_id ON designated_beneficiaries USING btree (user_id);
 
+CREATE INDEX index_diff_note_positions_on_namespace_id ON diff_note_positions USING btree (namespace_id);
+
 CREATE UNIQUE INDEX index_diff_note_positions_on_note_id_and_diff_type ON diff_note_positions USING btree (note_id, diff_type);
 
 CREATE INDEX index_dingtalk_tracker_data_on_integration_id ON dingtalk_tracker_data USING btree (integration_id);
@@ -46923,6 +46929,8 @@ CREATE TRIGGER set_namespace_for_system_note_metadata_on_insert BEFORE INSERT ON
 
 CREATE TRIGGER set_sharding_key_for_commit_user_mentions_on_insert_and_update BEFORE INSERT OR UPDATE ON commit_user_mentions FOR EACH ROW EXECUTE FUNCTION sync_sharding_key_with_notes_table();
 
+CREATE TRIGGER set_sharding_key_for_diff_note_positions_on_insert_and_update BEFORE INSERT OR UPDATE ON diff_note_positions FOR EACH ROW EXECUTE FUNCTION sync_sharding_key_with_notes_table();
+
 CREATE TRIGGER set_sharding_key_for_note_metadata_on_insert_and_update BEFORE INSERT OR UPDATE ON note_metadata FOR EACH ROW EXECUTE FUNCTION sync_sharding_key_with_notes_table();
 
 CREATE TRIGGER set_sharding_key_for_suggestions_on_insert_and_update BEFORE INSERT OR UPDATE ON suggestions FOR EACH ROW EXECUTE FUNCTION sync_sharding_key_with_notes_table();
@@ -48976,6 +48984,9 @@ ALTER TABLE ONLY issues
 ALTER TABLE ONLY clusters_managed_resources
     ADD CONSTRAINT fk_9c7b561962 FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY diff_note_positions
+    ADD CONSTRAINT fk_9ccec9c22a FOREIGN KEY (namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE NOT VALID;
+
 ALTER TABLE ONLY packages_conan_recipe_revisions
     ADD CONSTRAINT fk_9cdec8a86b FOREIGN KEY (package_id) REFERENCES packages_packages(id) ON DELETE CASCADE;
 
diff --git a/spec/lib/gitlab/database/sharding_key_spec.rb b/spec/lib/gitlab/database/sharding_key_spec.rb
index 40bb3be257f6e93ea8aab2aa3c826efa46aea2c7..078876aa5af39818d3f4a2cba34ad88a02e51131 100644
--- a/spec/lib/gitlab/database/sharding_key_spec.rb
+++ b/spec/lib/gitlab/database/sharding_key_spec.rb
@@ -335,7 +335,8 @@
       "suggestions" => "https://gitlab.com/gitlab-org/gitlab/-/issues/550696",
       "commit_user_mentions" => "https://gitlab.com/gitlab-org/gitlab/-/issues/550692",
       "note_metadata" => "https://gitlab.com/gitlab-org/gitlab/-/issues/550695",
-      "slack_integrations" => "https://gitlab.com/gitlab-org/gitlab/-/issues/524680"
+      "slack_integrations" => "https://gitlab.com/gitlab-org/gitlab/-/issues/524680",
+      "diff_note_positions" => "https://gitlab.com/gitlab-org/gitlab/-/issues/550693"
     }
 
     has_lfk = ->(lfks) { lfks.any? { |k| k.options[:column] == 'organization_id' && k.to_table == 'organizations' } }
diff --git a/spec/models/diff_note_position_spec.rb b/spec/models/diff_note_position_spec.rb
index 5ccf5d69ca70a2b33531f3302a7bada0461b95a7..78ce16928909bfb130c6b5cbb86940d2d05885a4 100644
--- a/spec/models/diff_note_position_spec.rb
+++ b/spec/models/diff_note_position_spec.rb
@@ -19,6 +19,22 @@
           expect(diff_note_position.line_code).to eq(line_code)
           expect(diff_note_position.diff_content_type).to eq('text')
         end
+
+        context 'with sharding key' do
+          it 'uses the note namespace_id as sharding key' do
+            note.update_column(:namespace_id, nil)
+            described_class.create_or_update_for(note, params)
+
+            expect(diff_note_position.namespace_id).to eq(note.project.project_namespace_id)
+          end
+
+          it 'uses the note project_id as sharding key' do
+            note.update_column(:project_id, nil)
+            described_class.create_or_update_for(note, params)
+
+            expect(diff_note_position.namespace_id).to eq(note.namespace_id)
+          end
+        end
       end
 
       context 'has a diff note position' do
@@ -30,6 +46,26 @@
           expect(diff_note_position.position).to eq(diff_position)
           expect(diff_note_position.line_code).to eq(line_code)
         end
+
+        context 'with sharding key' do
+          it 'uses the note project_id as sharding key' do
+            create(:diff_note_position, note: note)
+            note.update_column(:namespace_id, nil)
+            diff_note_position.update_column(:namespace_id, nil)
+            described_class.create_or_update_for(note, params)
+
+            expect(diff_note_position.reload.namespace_id).to eq(note.project.project_namespace_id)
+          end
+
+          it 'uses the note namespace_id as sharding key' do
+            create(:diff_note_position, note: note)
+            note.update_column(:project_id, nil)
+            diff_note_position.update_column(:namespace_id, nil)
+            described_class.create_or_update_for(note, params)
+
+            expect(diff_note_position.reload.namespace_id).to eq(note.namespace_id)
+          end
+        end
       end
     end
   end
diff --git a/spec/services/draft_notes/publish_service_spec.rb b/spec/services/draft_notes/publish_service_spec.rb
index 8d1dc64397de105822013c3005250b254712fca3..6452ba30ecaa199c8a3a65e5f2dcd15c26c2e6a6 100644
--- a/spec/services/draft_notes/publish_service_spec.rb
+++ b/spec/services/draft_notes/publish_service_spec.rb
@@ -195,6 +195,8 @@ def publish(draft: nil)
         notes = merge_request.notes.order(id: :asc)
         expect(notes.first.diff_note_positions).to be_any
         expect(notes.last.diff_note_positions).to be_any
+        expect(notes.flat_map(&:diff_note_positions).pluck(:namespace_id).uniq)
+          .to contain_exactly(project.project_namespace_id)
       end
 
       it 'keeps around the commits of each published note' do