diff --git a/app/models/system_note_metadata.rb b/app/models/system_note_metadata.rb
index e3d0fef546cfb5d296ca166ece93941f028500cc..cb9093412c5485b72277e8eb3a8c1275ad9e6313 100644
--- a/app/models/system_note_metadata.rb
+++ b/app/models/system_note_metadata.rb
@@ -71,4 +71,4 @@ def cross_reference_types
   end
 end
 
-SystemNoteMetadata.prepend_mod_with('SystemNoteMetadata')
+SystemNoteMetadata.prepend_mod
diff --git a/db/migrate/20250918203528_add_sharding_key_to_system_note_metadata.rb b/db/migrate/20250918203528_add_sharding_key_to_system_note_metadata.rb
new file mode 100644
index 0000000000000000000000000000000000000000..a187045d878460b6b79868ba55a2c74737e1b80f
--- /dev/null
+++ b/db/migrate/20250918203528_add_sharding_key_to_system_note_metadata.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class AddShardingKeyToSystemNoteMetadata < Gitlab::Database::Migration[2.3]
+  milestone '18.5'
+
+  def change
+    # rubocop:disable Migration/PreventAddingColumns -- Sharding key is an exception
+    add_column :system_note_metadata, :namespace_id, :bigint
+    add_column :system_note_metadata, :organization_id, :bigint
+    # rubocop:enable Migration/PreventAddingColumns
+  end
+end
diff --git a/db/migrate/20250918211138_add_sharding_key_trigger_on_system_note_metadata.rb b/db/migrate/20250918211138_add_sharding_key_trigger_on_system_note_metadata.rb
new file mode 100644
index 0000000000000000000000000000000000000000..82a2497cf30c89715e1b29cad2a4881fe857ba69
--- /dev/null
+++ b/db/migrate/20250918211138_add_sharding_key_trigger_on_system_note_metadata.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+class AddShardingKeyTriggerOnSystemNoteMetadata < Gitlab::Database::Migration[2.3]
+  include Gitlab::Database::SchemaHelpers
+
+  FUNCTION_NAME = 'get_sharding_key_from_notes_table'
+  TRIGGER_NAME = 'set_sharding_key_for_system_note_metadata_on_insert'
+
+  milestone '18.5'
+
+  def up
+    execute(<<~SQL)
+      CREATE OR REPLACE FUNCTION #{FUNCTION_NAME}()
+      RETURNS TRIGGER AS
+      $$
+      DECLARE
+        note_organization_id BIGINT;
+        note_project_id BIGINT;
+        note_namespace_id BIGINT;
+      BEGIN
+        IF NEW."note_id" IS NULL OR num_nonnulls(NEW."namespace_id", NEW."organization_id") = 1 THEN
+          RETURN NEW;
+        END IF;
+
+        SELECT "organization_id", "project_id", "namespace_id"
+        INTO note_organization_id, note_project_id, note_namespace_id
+        FROM "notes"
+        WHERE "id" = NEW."note_id";
+
+        IF note_organization_id IS NOT NULL THEN
+          NEW."organization_id" := note_organization_id;
+          NEW."namespace_id" := NULL;
+        ELSIF note_project_id IS NOT NULL THEN
+          SELECT "project_namespace_id" FROM "projects"
+          INTO NEW."namespace_id" WHERE "projects"."id" = note_project_id;
+          NEW."organization_id" := NULL;
+        ELSE
+          NEW."namespace_id" := note_namespace_id;
+          NEW."organization_id" := NULL;
+        END IF;
+
+        RETURN NEW;
+      END
+      $$ LANGUAGE PLPGSQL;
+    SQL
+
+    create_trigger(:system_note_metadata, TRIGGER_NAME, FUNCTION_NAME, fires: 'BEFORE INSERT')
+  end
+
+  def down
+    drop_trigger(:system_note_metadata, TRIGGER_NAME)
+
+    drop_function(FUNCTION_NAME)
+  end
+end
diff --git a/db/post_migrate/20250918221702_add_not_null_constraint_on_system_note_metadata_sharding_key.rb b/db/post_migrate/20250918221702_add_not_null_constraint_on_system_note_metadata_sharding_key.rb
new file mode 100644
index 0000000000000000000000000000000000000000..16e0f503cf5d11bc140706f9f7e4ae837704061d
--- /dev/null
+++ b/db/post_migrate/20250918221702_add_not_null_constraint_on_system_note_metadata_sharding_key.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class AddNotNullConstraintOnSystemNoteMetadataShardingKey < Gitlab::Database::Migration[2.3]
+  disable_ddl_transaction!
+  milestone '18.5'
+
+  def up
+    add_multi_column_not_null_constraint :system_note_metadata,
+      :namespace_id,
+      :organization_id,
+      validate: false
+  end
+
+  def down
+    remove_multi_column_not_null_constraint :system_note_metadata, :namespace_id, :organization_id
+  end
+end
diff --git a/db/post_migrate/20250918222201_add_sharding_key_indexes_on_system_note_metadata_async.rb b/db/post_migrate/20250918222201_add_sharding_key_indexes_on_system_note_metadata_async.rb
new file mode 100644
index 0000000000000000000000000000000000000000..c7942f04e602190c98a3237593053d88c25c1406
--- /dev/null
+++ b/db/post_migrate/20250918222201_add_sharding_key_indexes_on_system_note_metadata_async.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class AddShardingKeyIndexesOnSystemNoteMetadataAsync < Gitlab::Database::Migration[2.3]
+  NAMESPACE_INDEX = 'index_system_note_metadata_on_namespace_id'
+  ORGANIZATION_INDEX = 'index_system_note_metadata_on_organization_id'
+
+  milestone '18.5'
+
+  def up
+    # rubocop:disable Migration/PreventIndexCreation -- Sharding key is an exception
+    prepare_async_index :system_note_metadata, :namespace_id, name: NAMESPACE_INDEX
+    prepare_async_index :system_note_metadata, :organization_id, name: ORGANIZATION_INDEX
+    # rubocop:enable Migration/PreventIndexCreation
+  end
+
+  def down
+    unprepare_async_index :system_note_metadata, :namespace_id, name: NAMESPACE_INDEX
+    unprepare_async_index :system_note_metadata, :organization_id, name: ORGANIZATION_INDEX
+  end
+end
diff --git a/db/schema_migrations/20250918203528 b/db/schema_migrations/20250918203528
new file mode 100644
index 0000000000000000000000000000000000000000..6373b814cb0075f25ed7c8ea3e00feba7d5dcd82
--- /dev/null
+++ b/db/schema_migrations/20250918203528
@@ -0,0 +1 @@
+f487a5b0dbb9f19a497d45298beef4be958b97985bf8841c3d77094658afd345
\ No newline at end of file
diff --git a/db/schema_migrations/20250918211138 b/db/schema_migrations/20250918211138
new file mode 100644
index 0000000000000000000000000000000000000000..fd594bb6851242080d8cdcac3d95a9c250d598fb
--- /dev/null
+++ b/db/schema_migrations/20250918211138
@@ -0,0 +1 @@
+266ec6e26909ee142252e2a45c741d0e9aa096246c2247ff56ce783be94a71ad
\ No newline at end of file
diff --git a/db/schema_migrations/20250918221702 b/db/schema_migrations/20250918221702
new file mode 100644
index 0000000000000000000000000000000000000000..9d6c0ab8c25ce95411b2d15ae49eeec54b0f99b1
--- /dev/null
+++ b/db/schema_migrations/20250918221702
@@ -0,0 +1 @@
+763efab11d47b78d9cd28e22d5cdf96b14b9d7c6a006b621b065ea085e17cc23
\ No newline at end of file
diff --git a/db/schema_migrations/20250918222201 b/db/schema_migrations/20250918222201
new file mode 100644
index 0000000000000000000000000000000000000000..5cfdbed0aebe7a0332e1ecede35c38e97c1df5cb
--- /dev/null
+++ b/db/schema_migrations/20250918222201
@@ -0,0 +1 @@
+393eb5bf8df14469f8539edeb5baf698471ccad53b7712b897d7cb4a1d0cbd24
\ No newline at end of file
diff --git a/db/structure.sql b/db/structure.sql
index 1dcae9fa5ab71f000b413ba05969fac5cde298c0..d7c495c9cc2b91b6a4a3226635ece6c50515f83f 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -503,6 +503,39 @@ BEGIN
 END
 $$;
 
+CREATE FUNCTION get_sharding_key_from_notes_table() RETURNS trigger
+    LANGUAGE plpgsql
+    AS $$
+DECLARE
+  note_organization_id BIGINT;
+  note_project_id BIGINT;
+  note_namespace_id BIGINT;
+BEGIN
+  IF NEW."note_id" IS NULL OR num_nonnulls(NEW."namespace_id", NEW."organization_id") = 1 THEN
+    RETURN NEW;
+  END IF;
+
+  SELECT "organization_id", "project_id", "namespace_id"
+  INTO note_organization_id, note_project_id, note_namespace_id
+  FROM "notes"
+  WHERE "id" = NEW."note_id";
+
+  IF note_organization_id IS NOT NULL THEN
+    NEW."organization_id" := note_organization_id;
+    NEW."namespace_id" := NULL;
+  ELSIF note_project_id IS NOT NULL THEN
+    SELECT "project_namespace_id" FROM "projects"
+    INTO NEW."namespace_id" WHERE "projects"."id" = note_project_id;
+    NEW."organization_id" := NULL;
+  ELSE
+    NEW."namespace_id" := note_namespace_id;
+    NEW."organization_id" := NULL;
+  END IF;
+
+  RETURN NEW;
+END
+$$;
+
 CREATE FUNCTION gitlab_schema_prevent_write() RETURNS trigger
     LANGUAGE plpgsql
     AS $$
@@ -26425,7 +26458,9 @@ CREATE TABLE system_note_metadata (
     updated_at timestamp without time zone NOT NULL,
     description_version_id bigint,
     note_id bigint NOT NULL,
-    id bigint NOT NULL
+    id bigint NOT NULL,
+    namespace_id bigint,
+    organization_id bigint
 );
 
 CREATE SEQUENCE system_note_metadata_id_seq
@@ -32793,6 +32828,9 @@ ALTER TABLE sprints
 ALTER TABLE redirect_routes
     ADD CONSTRAINT check_e82ff70482 CHECK ((namespace_id IS NOT NULL)) NOT VALID;
 
+ALTER TABLE system_note_metadata
+    ADD CONSTRAINT check_f2c4e04565 CHECK ((num_nonnulls(namespace_id, organization_id) = 1)) NOT VALID;
+
 ALTER TABLE notes_archived
     ADD CONSTRAINT check_notes_archived_has_parent CHECK ((num_nonnulls(namespace_id, organization_id, project_id) >= 1)) NOT VALID;
 
@@ -46199,6 +46237,8 @@ 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_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();
 
 CREATE TRIGGER sync_sent_notifications_to_part AFTER INSERT ON sent_notifications FOR EACH ROW EXECUTE FUNCTION sync_to_p_sent_notifications_table();
diff --git a/spec/db/schema_spec.rb b/spec/db/schema_spec.rb
index 5a0623378d213e1c954795db47d87ba13790d51e..7d4125fb5c05b55345ff55f0a133d24343657328 100644
--- a/spec/db/schema_spec.rb
+++ b/spec/db/schema_spec.rb
@@ -284,6 +284,7 @@
       security_finding_token_statuses: %w[security_finding_id project_id],
       system_access_group_microsoft_graph_access_tokens: %w[temp_source_id], # temporary column that is not a foreign key
       system_access_group_microsoft_applications: %w[temp_source_id], # temporary column that is not a foreign key
+      system_note_metadata: %w[namespace_id organization_id], # Adding FK after indexes are created over the weekend
       subscription_user_add_on_assignment_versions: %w[item_id user_id purchase_id], # Managed by paper_trail gem, no need for FK on the historical data
       virtual_registries_packages_maven_cache_entries: %w[group_id], # We can't use a foreign key due to object storage references
       # system_defined_status_id reference to fixed items model which is stored in code
diff --git a/spec/lib/gitlab/database/sharding_key_spec.rb b/spec/lib/gitlab/database/sharding_key_spec.rb
index f3da05caf6af29827ba44146f9fdee53c0b9bff9..2828063eb8e0e5d27b4cc4633e675856fb9c52d8 100644
--- a/spec/lib/gitlab/database/sharding_key_spec.rb
+++ b/spec/lib/gitlab/database/sharding_key_spec.rb
@@ -322,7 +322,8 @@
       "labels" => "https://gitlab.com/gitlab-org/gitlab/-/issues/563889",
       "notes" => "https://gitlab.com/gitlab-org/gitlab/-/issues/569521",
       "notes_archived" => "https://gitlab.com/gitlab-org/gitlab/-/issues/569521",
-      "jira_connect_installations" => "https://gitlab.com/gitlab-org/gitlab/-/issues/524682"
+      "jira_connect_installations" => "https://gitlab.com/gitlab-org/gitlab/-/issues/524682",
+      "system_note_metadata" => "https://gitlab.com/gitlab-org/gitlab/-/issues/571215"
     }
     has_lfk = ->(lfks) { lfks.any? { |k| k.options[:column] == 'organization_id' && k.to_table == 'organizations' } }
 
diff --git a/spec/models/system_note_metadata_spec.rb b/spec/models/system_note_metadata_spec.rb
index 6a770b34d3e244066b7fbe000e263afff2d0b99f..65a70907d854d6bf6d4fc79392d81b77f22371e8 100644
--- a/spec/models/system_note_metadata_spec.rb
+++ b/spec/models/system_note_metadata_spec.rb
@@ -84,4 +84,30 @@
       end
     end
   end
+
+  describe 'ensure sharding key trigger' do
+    let_it_be(:group) { create(:group) }
+    let_it_be(:project) { create(:project, group: group) }
+    let_it_be(:personal_snippet) { create(:personal_snippet) }
+
+    subject { create(:system_note_metadata, note: note).reload.values_at(:namespace_id, :organization_id) }
+
+    context 'when associated note belongs to an organization' do
+      let(:note) { create(:note_on_personal_snippet, noteable: personal_snippet) }
+
+      it { is_expected.to eq([nil, personal_snippet.organization_id]) }
+    end
+
+    context 'when associated note belongs to a project and namespace' do
+      let(:note) { create(:note, noteable: create(:issue, project: project), project: project) }
+
+      it { is_expected.to eq([project.project_namespace_id, nil]) }
+    end
+
+    context 'when associated note belongs only to a namespace' do
+      let(:note) { create(:note, noteable: create(:issue, :group_level, namespace: group), project_id: nil) }
+
+      it { is_expected.to eq([group.id, nil]) }
+    end
+  end
 end