diff --git a/src/backend/app/auth/providers/osm.py b/src/backend/app/auth/providers/osm.py
index 7d860a6ab..8ee1ec125 100644
--- a/src/backend/app/auth/providers/osm.py
+++ b/src/backend/app/auth/providers/osm.py
@@ -157,3 +157,20 @@ def send_osm_message(
     else:
         msg = "Sending message via OSM failed"
         log.error(f"{msg}: {response.text}")
+
+
+async def check_osm_user(osm_username: str):
+    """Check if the user is an OSM user based on their username."""
+    osm_url = f"https://www.openstreetmap.org/user/{osm_username}/"
+
+    user_exists = False
+    try:
+        response = requests.get(osm_url)
+        if response.status_code == 200:
+            user_exists = True
+    except Exception as e:
+        log.exception(
+            f"Failed to check if user exists on OSM. Error: {e}",
+            stack_info=True,
+        )
+    return user_exists
diff --git a/src/backend/app/projects/project_crud.py b/src/backend/app/projects/project_crud.py
index 7bb316303..cc24d6fdc 100644
--- a/src/backend/app/projects/project_crud.py
+++ b/src/backend/app/projects/project_crud.py
@@ -967,3 +967,36 @@ async def send_project_manager_message(
         body=message_content,
     )
     log.info(f"Message sent to new project manager ({new_manager.username}).")
+
+
+async def send_invitation_message(
+    request: Request,
+    project: DbProject,
+    invitee_username: str,
+    osm_auth: Auth,
+):
+    """Send an invitation message to a user to join a project."""
+    log.info(f"Sending invitation message to osm user ({invitee_username}).")
+
+    osm_token = get_osm_token(request, osm_auth)
+
+    project_url = f"{settings.FMTM_DOMAIN}/project/{project.id}"
+    if not project_url.startswith("http"):
+        project_url = f"https://{project_url}"
+
+    message_content = dedent(f"""
+        You have been invited to join the project **{project.name}**.
+
+        Please click this link:
+        [Project]({project_url})
+
+        Thank you for being a part of our platform!
+    """)
+
+    send_osm_message(
+        osm_token=osm_token,
+        osm_username=invitee_username,
+        title=f"You have been invited to join the project {project.name}",
+        body=message_content,
+    )
+    log.info(f"Invitation message sent to osm user ({invitee_username}).")
diff --git a/src/backend/app/projects/project_routes.py b/src/backend/app/projects/project_routes.py
index 4dcba3985..1c27420ae 100644
--- a/src/backend/app/projects/project_routes.py
+++ b/src/backend/app/projects/project_routes.py
@@ -48,7 +48,7 @@
 
 from app.auth.auth_deps import login_required, mapper_login_required
 from app.auth.auth_schemas import AuthUser, OrgUserDict, ProjectUserDict
-from app.auth.providers.osm import init_osm_auth
+from app.auth.providers.osm import check_osm_user, init_osm_auth
 from app.auth.roles import mapper, org_admin, project_manager
 from app.central import central_crud, central_deps, central_schemas
 from app.config import settings
@@ -759,6 +759,32 @@ async def add_new_project_manager(
     return Response(status_code=HTTPStatus.OK)
 
 
+@router.post("/invite-new-user")
+async def invite_new_user(
+    request: Request,
+    background_tasks: BackgroundTasks,
+    project: Annotated[DbProject, Depends(project_deps.get_project)],
+    invitee_username: str,
+    osm_auth=Depends(init_osm_auth),
+):
+    """Invite a new user to a project."""
+    user_exists = await check_osm_user(invitee_username)
+
+    if not user_exists:
+        raise HTTPException(
+            status_code=HTTPStatus.NOT_FOUND,
+            detail="User does not exist on Open Street Map",
+        )
+    background_tasks.add_task(
+        project_crud.send_invitation_message,
+        request=request,
+        project=project,
+        invitee_username=invitee_username,
+        osm_auth=osm_auth,
+    )
+    return Response(status_code=HTTPStatus.OK)
+
+
 @router.post("/update-form")
 async def update_project_form(
     xlsform: Annotated[BytesIO, Depends(central_deps.read_xlsform)],