diff --git a/infrastructure/s3/s3_client.py b/infrastructure/s3/s3_client.py
index 7e26c790b..5d5dc55ae 100644
--- a/infrastructure/s3/s3_client.py
+++ b/infrastructure/s3/s3_client.py
@@ -25,7 +25,8 @@ class S3Client:
         """Upload a file from local disk, using boto's managed transfer so a
         large object (a multi-GB Download Package ZIP, ADR-0060) is streamed in
         multipart from ``/tmp`` rather than held in memory."""
-        raise NotImplementedError
+        self._client.upload_file(Filename=local_path, Bucket=self._bucket, Key=key)
+        return f"s3://{self._bucket}/{key}"
 
     def generate_presigned_url(self, key: str, expires_in: int) -> str:
         """A time-limited URL that lets the holder GET this object without AWS