diff --git a/db/migrate/20251007102142_add_sharding_key_to_suggestions.rb b/db/migrate/20251007102142_add_sharding_key_to_suggestions.rb
new file mode 100644
index 0000000000000000000000000000000000000000..5b2b1ae28ae81aef403b73f24b59a9639b480b2c
--- /dev/null
+++ b/db/migrate/20251007102142_add_sharding_key_to_suggestions.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class AddShardingKeyToSuggestions < Gitlab::Database::Migration[2.3]
+  milestone '18.6'
+
+  def change
+    add_column :suggestions, :namespace_id, :bigint
+  end
+end
diff --git a/db/migrate/20251007102313_add_sharding_key_trigger_on_suggestions.rb b/db/migrate/20251007102313_add_sharding_key_trigger_on_suggestions.rb
new file mode 100644
index 0000000000000000000000000000000000000000..4330af3d74750764541238770ce98f01866f7e97
--- /dev/null
+++ b/db/migrate/20251007102313_add_sharding_key_trigger_on_suggestions.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+class AddShardingKeyTriggerOnSuggestions < Gitlab::Database::Migration[2.3]
+  include Gitlab::Database::SchemaHelpers
+
+  FUNCTION_NAME = 'sync_sharding_key_with_notes_table'
+  TRIGGER_NAME = 'set_sharding_key_for_suggestions_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(:suggestions, TRIGGER_NAME, FUNCTION_NAME, fires: 'BEFORE INSERT OR UPDATE')
+  end
+
+  def down
+    drop_trigger(:suggestions, TRIGGER_NAME)
+
+    drop_function(FUNCTION_NAME)
+  end
+end
diff --git a/db/post_migrate/20251007111103_add_not_null_constraint_on_suggestions_sharding_key.rb b/db/post_migrate/20251007111103_add_not_null_constraint_on_suggestions_sharding_key.rb
new file mode 100644
index 0000000000000000000000000000000000000000..c139dd036d53c14379d3cf992497b2f6e00a7cba
--- /dev/null
+++ b/db/post_migrate/20251007111103_add_not_null_constraint_on_suggestions_sharding_key.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class AddNotNullConstraintOnSuggestionsShardingKey < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.6'
+
+  def up
+    add_not_null_constraint :suggestions, :namespace_id, validate: false
+  end
+
+  def down
+    remove_not_null_constraint :suggestions, :namespace_id
+  end
+end
diff --git a/db/post_migrate/20251007111146_add_sharding_key_index_on_suggestions.rb b/db/post_migrate/20251007111146_add_sharding_key_index_on_suggestions.rb
new file mode 100644
index 0000000000000000000000000000000000000000..15cb031e7cf9ed3c5feb97a40ceab7dde11742d0
--- /dev/null
+++ b/db/post_migrate/20251007111146_add_sharding_key_index_on_suggestions.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class AddShardingKeyIndexOnSuggestions < Gitlab::Database::Migration[2.3]
+  INDEX_NAME = 'index_suggestions_on_namespace_id'
+
+  milestone '18.6'
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :suggestions, :namespace_id, name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :suggestions, INDEX_NAME
+  end
+end
diff --git a/db/post_migrate/20251013085124_add_suggestions_namespace_id_foreign_key.rb b/db/post_migrate/20251013085124_add_suggestions_namespace_id_foreign_key.rb
new file mode 100644
index 0000000000000000000000000000000000000000..56cccbf895b598a52788056e080e1435e7b55849
--- /dev/null
+++ b/db/post_migrate/20251013085124_add_suggestions_namespace_id_foreign_key.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class AddSuggestionsNamespaceIdForeignKey < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.6'
+
+  def up
+    add_concurrent_foreign_key :suggestions,
+      :namespaces,
+      column: :namespace_id,
+      reverse_lock_order: true,
+      validate: false
+  end
+
+  def down
+    with_lock_retries do
+      remove_foreign_key_if_exists(:suggestions, column: :namespace_id)
+    end
+  end
+end
diff --git a/db/schema_migrations/20251007102142 b/db/schema_migrations/20251007102142
new file mode 100644
index 0000000000000000000000000000000000000000..675bfd9267588dade407332cd707ba44558361fb
--- /dev/null
+++ b/db/schema_migrations/20251007102142
@@ -0,0 +1 @@
+411080c716f68f0ff85dd6eebf107ec03f826cb518a8632ab998530c806d07b5
\ No newline at end of file
diff --git a/db/schema_migrations/20251007102313 b/db/schema_migrations/20251007102313
new file mode 100644
index 0000000000000000000000000000000000000000..1ea6c3997b536514b8781a8523adbb39b42db160
--- /dev/null
+++ b/db/schema_migrations/20251007102313
@@ -0,0 +1 @@
+c1ee5c4aced2c5e2c05c142582a0217d1b34a0d6ecad235953d59cc9c103003f
\ No newline at end of file
diff --git a/db/schema_migrations/20251007111103 b/db/schema_migrations/20251007111103
new file mode 100644
index 0000000000000000000000000000000000000000..b5b5a362e0ca3c167a7ffe6a392bb5d9befc10a8
--- /dev/null
+++ b/db/schema_migrations/20251007111103
@@ -0,0 +1 @@
+66eaa55375e15abe2666bb07d5dbba834072c90ca0feaaeccc14a46aa934ba01
\ No newline at end of file
diff --git a/db/schema_migrations/20251007111146 b/db/schema_migrations/20251007111146
new file mode 100644
index 0000000000000000000000000000000000000000..66dcea3c60df584127de6bfaa6e5bd750cccdb19
--- /dev/null
+++ b/db/schema_migrations/20251007111146
@@ -0,0 +1 @@
+7a2ff0a3347c2b404ccf84fc3462eaf2301d92c073f668c22bedc4f48dfafd8a
\ No newline at end of file
diff --git a/db/schema_migrations/20251013085124 b/db/schema_migrations/20251013085124
new file mode 100644
index 0000000000000000000000000000000000000000..dd6d68b91b697bb49ea1236f666eb368fcf7050a
--- /dev/null
+++ b/db/schema_migrations/20251013085124
@@ -0,0 +1 @@
+f5d223d252b3be6fb5c72ad1281f928a08525e997697de690c82ac746c57255a
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index b9946ff29f5399f6e334beb906c49a2765e8384d..75927edb60ba2093ea964b23c96037345ff65d98 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -1113,6 +1113,33 @@ RETURN NEW;
 END
 $$;
 
+CREATE FUNCTION sync_sharding_key_with_notes_table() RETURNS trigger
+    LANGUAGE plpgsql
+    AS $$
+DECLARE
+  note_project_id BIGINT;
+  note_namespace_id BIGINT;
+BEGIN
+  IF NEW."note_id" IS NULL OR NEW."namespace_id" IS NOT NULL THEN
+    RETURN NEW;
+  END IF;
+
+  SELECT "project_id", "namespace_id"
+  INTO note_project_id, note_namespace_id
+  FROM "notes"
+  WHERE "id" = NEW."note_id";
+
+  IF note_project_id IS NOT NULL THEN
+    SELECT "project_namespace_id" FROM "projects"
+    INTO NEW."namespace_id" WHERE "projects"."id" = note_project_id;
+  ELSE
+    NEW."namespace_id" := note_namespace_id;
+  END IF;
+
+  RETURN NEW;
+END
+$$;
+
 CREATE FUNCTION sync_to_p_sent_notifications_table() RETURNS trigger
     LANGUAGE plpgsql
     AS $$
@@ -26564,7 +26591,8 @@ CREATE TABLE suggestions (
     lines_above integer DEFAULT 0 NOT NULL,
     lines_below integer DEFAULT 0 NOT NULL,
     outdated boolean DEFAULT false NOT NULL,
-    note_id bigint NOT NULL
+    note_id bigint NOT NULL,
+    namespace_id bigint
 );
 
 CREATE SEQUENCE suggestions_id_seq
@@ -33205,6 +33233,9 @@ ALTER TABLE packages_packages
 ALTER TABLE sprints
     ADD CONSTRAINT check_df3816aed7 CHECK ((due_date IS NOT NULL)) NOT VALID;
 
+ALTER TABLE suggestions
+    ADD CONSTRAINT check_e69372e45f CHECK ((namespace_id IS NOT NULL)) NOT VALID;
+
 ALTER TABLE redirect_routes
     ADD CONSTRAINT check_e82ff70482 CHECK ((namespace_id IS NOT NULL)) NOT VALID;
 
@@ -42463,6 +42494,8 @@ CREATE INDEX index_subscriptions_on_user ON subscriptions USING btree (user_id);
 
 CREATE INDEX index_successful_authentication_events_for_metrics ON authentication_events USING btree (user_id, provider, created_at) WHERE (result = 1);
 
+CREATE INDEX index_suggestions_on_namespace_id ON suggestions USING btree (namespace_id);
+
 CREATE UNIQUE INDEX index_suggestions_on_note_id_and_relative_order ON suggestions USING btree (note_id, relative_order);
 
 CREATE UNIQUE INDEX index_system_access_group_microsoft_applications_on_group_id ON system_access_group_microsoft_applications USING btree (group_id);
@@ -46851,6 +46884,8 @@ CREATE TRIGGER projects_loose_fk_trigger AFTER DELETE ON projects REFERENCING OL
 
 CREATE TRIGGER push_rules_loose_fk_trigger AFTER DELETE ON push_rules REFERENCING OLD TABLE AS old_table FOR EACH STATEMENT EXECUTE FUNCTION insert_into_loose_foreign_keys_deleted_records();
 
+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();
+
 CREATE TRIGGER set_sharding_key_for_system_note_metadata_on_insert BEFORE INSERT ON system_note_metadata FOR EACH ROW EXECUTE FUNCTION get_sharding_key_from_notes_table();
 
 CREATE TRIGGER sync_project_authorizations_to_migration AFTER INSERT OR DELETE OR UPDATE ON project_authorizations FOR EACH ROW EXECUTE FUNCTION sync_project_authorizations_to_migration_table();
@@ -47960,6 +47995,9 @@ ALTER TABLE ONLY namespaces
 ALTER TABLE ONLY saml_providers
     ADD CONSTRAINT fk_351dde3a84 FOREIGN KEY (member_role_id) REFERENCES member_roles(id) ON DELETE SET NULL;
 
+ALTER TABLE ONLY suggestions
+    ADD CONSTRAINT fk_35c950f0d6 FOREIGN KEY (namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE NOT VALID;
+
 ALTER TABLE ONLY approval_merge_request_rules_users
     ADD CONSTRAINT fk_35e88790f5 FOREIGN KEY (project_id) REFERENCES projects(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 3db66e3b039e86d60c6f416697b2afe926386923..0194ea9f513cabd056ee2742a5ab593c0d8a25ec 100644
--- a/spec/lib/gitlab/database/sharding_key_spec.rb
+++ b/spec/lib/gitlab/database/sharding_key_spec.rb
@@ -328,7 +328,8 @@
       "notes_archived" => "https://gitlab.com/gitlab-org/gitlab/-/issues/569521",
       "system_note_metadata" => "https://gitlab.com/gitlab-org/gitlab/-/issues/571215",
       "note_diff_files" => "https://gitlab.com/gitlab-org/gitlab/-/issues/550694",
-      "keys" => "https://gitlab.com/gitlab-org/gitlab/-/issues/553463"
+      "keys" => "https://gitlab.com/gitlab-org/gitlab/-/issues/553463",
+      "suggestions" => "https://gitlab.com/gitlab-org/gitlab/-/issues/550696"
     }
 
     has_lfk = ->(lfks) { lfks.any? { |k| k.options[:column] == 'organization_id' && k.to_table == 'organizations' } }
diff --git a/spec/models/suggestion_spec.rb b/spec/models/suggestion_spec.rb
index 4f91908264fc00241a38d0c9fbb2854036eab5db..364a240821b370510bd622cbf2adc86a574de962 100644
--- a/spec/models/suggestion_spec.rb
+++ b/spec/models/suggestion_spec.rb
@@ -182,4 +182,19 @@
       it { is_expected.to eq(false) }
     end
   end
+
+  describe 'ensure sharding key trigger' do
+    let_it_be(:diff_note) { create(:diff_note_on_merge_request) }
+
+    it 'syncs `namespace_id` with note on create' do
+      expect(create(:suggestion, note: diff_note).reload.namespace_id).to eq(diff_note.project.project_namespace_id)
+    end
+
+    it 'syncs `namespace_id` with note on update' do
+      existing_suggestion = create(:suggestion, note: diff_note)
+      existing_suggestion.update!(namespace_id: nil)
+
+      expect(existing_suggestion.reload.namespace_id).to eq(diff_note.project.project_namespace_id)
+    end
+  end
 end