diff --git a/changelog.d/17304.feature b/changelog.d/17304.feature
new file mode 100644
index 00000000000..a969d8bf585
--- /dev/null
+++ b/changelog.d/17304.feature
@@ -0,0 +1,2 @@
+`register_new_matrix_user` now supports a --exists-ok flag to allow registration of users that already exist in the database.
+This is useful for scripts that bootstrap user accounts with initial passwords.
diff --git a/debian/changelog b/debian/changelog
index 55e17bd8682..731eacf20f3 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,6 +1,6 @@
 matrix-synapse-py3 (1.109.0+nmu1) UNRELEASED; urgency=medium
 
-  * `register_new_matrix_user` now supports a --password-file flag.
+  * `register_new_matrix_user` now supports a --password-file and a --exists-ok flag.
 
  -- Synapse Packaging team <packages@matrix.org>  Tue, 18 Jun 2024 13:29:36 +0100
 
diff --git a/debian/register_new_matrix_user.ronn b/debian/register_new_matrix_user.ronn
index 963e67c0041..aa305ec6718 100644
--- a/debian/register_new_matrix_user.ronn
+++ b/debian/register_new_matrix_user.ronn
@@ -48,6 +48,9 @@ A sample YAML file accepted by `register_new_matrix_user` is described below:
     Shared secret as defined in server config file. This is an optional
     parameter as it can be also supplied via the YAML file.
 
+  * `--exists-ok`:
+    Do not fail if the user already exists. The user account will be not updated in this case.
+
   * `server_url`:
     URL of the home server. Defaults to 'https://localhost:8448'.
 
diff --git a/synapse/_scripts/register_new_matrix_user.py b/synapse/_scripts/register_new_matrix_user.py
index 972b35e2dc0..14cb21c7fb4 100644
--- a/synapse/_scripts/register_new_matrix_user.py
+++ b/synapse/_scripts/register_new_matrix_user.py
@@ -52,6 +52,7 @@ def request_registration(
     user_type: Optional[str] = None,
     _print: Callable[[str], None] = print,
     exit: Callable[[int], None] = sys.exit,
+    exists_ok: bool = False,
 ) -> None:
     url = "%s/_synapse/admin/v1/register" % (server_location.rstrip("/"),)
 
@@ -97,6 +98,10 @@ def request_registration(
     r = requests.post(url, json=data)
 
     if r.status_code != 200:
+        response = r.json()
+        if exists_ok and response["errcode"] == "M_USER_IN_USE":
+            _print("User already exists. Skipping.")
+            return
         _print("ERROR! Received %d %s" % (r.status_code, r.reason))
         if 400 <= r.status_code < 500:
             try:
@@ -115,6 +120,7 @@ def register_new_user(
     shared_secret: str,
     admin: Optional[bool],
     user_type: Optional[str],
+    exists_ok: bool = False,
 ) -> None:
     if not user:
         try:
@@ -154,7 +160,13 @@ def register_new_user(
             admin = False
 
     request_registration(
-        user, password, server_location, shared_secret, bool(admin), user_type
+        user,
+        password,
+        server_location,
+        shared_secret,
+        bool(admin),
+        user_type,
+        exists_ok=exists_ok,
     )
 
 
@@ -173,6 +185,11 @@ def main() -> None:
         default=None,
         help="Local part of the new user. Will prompt if omitted.",
     )
+    parser.add_argument(
+        "--exists-ok",
+        action="store_true",
+        help="Do not fail if user already exists.",
+    )
     password_group = parser.add_mutually_exclusive_group()
     password_group.add_argument(
         "-p",
@@ -192,6 +209,7 @@ def main() -> None:
         default=None,
         help="User type as specified in synapse.api.constants.UserTypes",
     )
+
     admin_group = parser.add_mutually_exclusive_group()
     admin_group.add_argument(
         "-a",
@@ -281,7 +299,15 @@ def main() -> None:
     if args.admin or args.no_admin:
         admin = args.admin
 
-    register_new_user(args.user, password, server_url, secret, admin, args.user_type)
+    register_new_user(
+        args.user,
+        password,
+        server_url,
+        secret,
+        admin,
+        args.user_type,
+        exists_ok=args.exists_ok,
+    )
 
 
 def _read_file(file_path: Any, config_path: str) -> str: