diff --git a/.conda/meorg_client_dev.yaml b/.conda/meorg_client_dev.yaml
index 04c31b5..1990255 100644
--- a/.conda/meorg_client_dev.yaml
+++ b/.conda/meorg_client_dev.yaml
@@ -15,5 +15,6 @@ dependencies:
   - pytest
   - black
   - ruff
+  - pandas>=2.2.2
   - pip:
     - -r mkdocs-requirements.txt
\ No newline at end of file
diff --git a/.conda/meta.yaml b/.conda/meta.yaml
index ae7a048..7e95724 100644
--- a/.conda/meta.yaml
+++ b/.conda/meta.yaml
@@ -26,6 +26,7 @@ requirements:
     - requests >=2.31.0
     - click >=8.1.7
     - PyYAML >=6.0.1
+    - pandas >=2.2.2
 
 test:
   imports:
diff --git a/meorg_client/cli.py b/meorg_client/cli.py
index ba74525..6ae9267 100644
--- a/meorg_client/cli.py
+++ b/meorg_client/cli.py
@@ -109,19 +109,31 @@ def list_endpoints():
 
 @click.command("upload")
 @click.argument("file_path", nargs=-1)
-def file_upload(file_path: tuple):
+@click.option(
+    "--attach_to",
+    default=None,
+    help="Supply a model output id to immediately attach the file to.",
+)
+def file_upload(file_path, attach_to=None):
     """
     Upload a file to the server.
 
     Prints Job ID on success, which is used by file-status to check transfer status.
+
+    If attach_to is used then no ID is returned.
     """
     client = _get_client()
 
     # Upload the file, get the job ID
-    response = _call(client.upload_files, files=list(file_path))
-    files = response.get("data").get("files")
-    for f in files:
-        click.echo(f.get("file"))
+    response = _call(client.upload_files, files=list(file_path), attach_to=attach_to)
+
+    # Different logic if we are attaching to a model output immediately
+    if not attach_to:
+        files = response.get("data").get("files")
+        for f in files:
+            click.echo(f.get("file"))
+    else:
+        click.echo("SUCCESS")
 
 
 @click.command("upload_parallel")
@@ -129,7 +141,12 @@ def file_upload(file_path: tuple):
 @click.option(
     "-n", default=2, help="Number of simultaneous parallel uploads (default=2)."
 )
-def file_upload_parallel(file_paths: tuple, n: int = 2):
+@click.option(
+    "--attach_to",
+    default=None,
+    help="Supply a model output id to immediately attach the file to.",
+)
+def file_upload_parallel(file_paths: tuple, n: int = 2, attach_to: str = None):
     """Upload files in parallel.
 
     Parameters
diff --git a/meorg_client/client.py b/meorg_client/client.py
index 70834fd..85a7687 100644
--- a/meorg_client/client.py
+++ b/meorg_client/client.py
@@ -10,9 +10,9 @@
 import meorg_client.endpoints as endpoints
 import meorg_client.exceptions as mx
 import meorg_client.utilities as mu
+import meorg_client.parallel as meop
 import mimetypes as mt
 from pathlib import Path
-from multiprocessing import Pool
 
 
 class Client:
@@ -217,7 +217,9 @@ def logout(self):
             self.headers.pop("X-User-Id", None)
             self.headers.pop("X-Auth-Token", None)
 
-    def upload_files_parallel(self, files: Union[str, Path, list], n: int = 2):
+    def upload_files_parallel(
+        self, files: Union[str, Path, list], n: int = 2, attach_to: str = None
+    ):
         """Upload files in parallel.
 
         Parameters
@@ -226,6 +228,8 @@ def upload_files_parallel(self, files: Union[str, Path, list], n: int = 2):
             A path to a file, or a list of paths.
         n : int, optional
             Number of threads to use, by default 2.
+        attach_to : str, optional
+            Module output id to attach to, by default None.
 
         Returns
         -------
@@ -242,14 +246,16 @@ def upload_files_parallel(self, files: Union[str, Path, list], n: int = 2):
 
         # Do the parallel upload
         responses = None
-        with Pool(processes=n) as pool:
-            responses = pool.map(self.upload_files, files)
+        responses = meop.parallelise(
+            self.upload_files, n, files=files, attach_to=attach_to
+        )
 
         return responses
 
     def upload_files(
         self,
         files: Union[str, Path],
+        attach_to: str = None,
     ) -> Union[dict, requests.Response]:
         """Upload a file.
 
@@ -257,6 +263,8 @@ def upload_files(
         ----------
         files : path-like, list
             Path to the file, or a list containing paths.
+        attach_to : str, optional
+            Optional model_output_id to attach the files to, by default None
 
         Returns
         -------
@@ -309,6 +317,13 @@ def upload_files(
         for fd in payload:
             fd[1][1].close()
 
+        # Automatically attach to a model output
+        if attach_to:
+
+            _ = self.attach_files_to_model_output(
+                attach_to, files=mu.get_uploaded_file_ids(response)
+            )
+
         return response
 
     def list_files(self, id: str) -> Union[dict, requests.Response]:
diff --git a/meorg_client/parallel.py b/meorg_client/parallel.py
new file mode 100644
index 0000000..1962e2d
--- /dev/null
+++ b/meorg_client/parallel.py
@@ -0,0 +1,66 @@
+"""Methods for parallel execution."""
+
+import pandas as pd
+import multiprocessing as mp
+
+
+def _execute(mp_args: tuple):
+    """Execute an instance of the parallel function.
+
+    Parameters
+    ----------
+    mp_args : tuple
+        2-tuple consisting of a callable and an arguments dictionary.
+
+    Returns
+    -------
+    mixed
+        Returning value of the callable.
+    """
+    return mp_args[0](**mp_args[1])
+
+
+def _convert_kwargs(**kwargs):
+    """Convert a dict of lists and scalars into even lists for parallel execution.
+
+    Returns
+    -------
+    dict
+        A dictionary of lists of arguments.
+    """
+    return pd.DataFrame(kwargs).to_dict("records")
+
+
+def parallelise(func: callable, num_threads: int, **kwargs):
+    """Execute `func` in parallel over `num_threads`.
+
+    Parameters
+    ----------
+    func : callable
+        Function to parallelise.
+    num_threads : int
+        Number of threads.
+    **kwargs :
+        Keyword arguments for `func` all lists must have equal length, scalars will be converted to lists.
+
+    Returns
+    -------
+    mixed
+        Returning value of `func`.
+    """
+
+    # Convert the kwargs to argument list of dicts
+    mp_args = _convert_kwargs(**kwargs)
+
+    # Attach the function pointer as the first argument
+    mp_args = [[func, mp_arg] for mp_arg in mp_args]
+
+    # Start with empty results
+    results = None
+
+    # Establish a pool of workers (blocking)
+    with mp.Pool(processes=num_threads) as pool:
+        results = pool.map(_execute, mp_args)
+
+    # Return the results
+    return results
diff --git a/meorg_client/tests/test_cli.py b/meorg_client/tests/test_cli.py
index fe2fb2d..35423c0 100644
--- a/meorg_client/tests/test_cli.py
+++ b/meorg_client/tests/test_cli.py
@@ -89,3 +89,22 @@ def test_file_attach(runner):
     )
 
     assert result.exit_code == 0
+
+
+def test_file_upload_with_attach(runner, test_filepath):
+    """Test file upload with attachment via CLI."""
+    model_output_id = store.get("model_output_id")
+    result = runner.invoke(
+        cli.file_upload, [test_filepath, test_filepath, "--attach_to", model_output_id]
+    )
+    assert result.exit_code == 0
+
+
+def test_file_upload_parallel_with_attach(runner, test_filepath):
+    """Test file upload with attachment via CLI."""
+    model_output_id = store.get("model_output_id")
+    result = runner.invoke(
+        cli.file_upload_parallel,
+        [test_filepath, test_filepath, "--attach_to", model_output_id],
+    )
+    assert result.exit_code == 0
diff --git a/meorg_client/tests/test_client.py b/meorg_client/tests/test_client.py
index 6146680..b2a964a 100644
--- a/meorg_client/tests/test_client.py
+++ b/meorg_client/tests/test_client.py
@@ -40,6 +40,10 @@ def _get_authenticated_client() -> Client:
     return client
 
 
+def _get_test_file():
+    return os.path.join(mu.get_installed_data_root(), "test/test.txt")
+
+
 @pytest.fixture
 def client() -> Client:
     return _get_authenticated_client()
@@ -151,6 +155,13 @@ def test_upload_file_large(client: Client):
     assert client.success()
 
 
+def test_upload_files_with_attach(client: Client):
+    """Test that the upload can also attach in the same method call."""
+    filepath = _get_test_file()
+    _ = client.upload_files([filepath, filepath], attach_to=client._model_output_id)
+    assert client.success()
+
+
 def test_upload_file_parallel(client: Client, test_filepath: str):
     """Test the uploading of a file."""
     # Upload the file
@@ -162,6 +173,19 @@ def test_upload_file_parallel(client: Client, test_filepath: str):
     )
 
 
+def test_upload_file_parallel_with_attach(client: Client, test_filepath: str):
+    """Test the uploading of a file with a model output ID to attach."""
+    # Upload the file
+    responses = client.upload_files_parallel(
+        [test_filepath, test_filepath], n=2, attach_to=client._model_output_id
+    )
+
+    # Make sure it worked
+    assert all(
+        [response.get("data").get("files")[0].get("file") for response in responses]
+    )
+
+
 def test_logout(client: Client):
     """Test logout."""
     client.logout()
diff --git a/meorg_client/utilities.py b/meorg_client/utilities.py
index 9bd1336..302803d 100644
--- a/meorg_client/utilities.py
+++ b/meorg_client/utilities.py
@@ -84,3 +84,20 @@ def ensure_list(obj):
         The object as a list, if it is not already.
     """
     return obj if isinstance(obj, list) else [obj]
+
+
+def get_uploaded_file_ids(response):
+    """Get the file ids out of the response object.
+
+    Parameters
+    ----------
+    response : dict
+        Response dictionary from a upload call.
+
+    Returns
+    -------
+    list
+        List of file ids.
+    """
+    file_ids = [f.get("file") for f in response.get("data").get("files")]
+    return file_ids
diff --git a/pyproject.toml b/pyproject.toml
index 9678059..d6fc847 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,7 +23,8 @@ dependencies = [
     "requests>=2.31.0",
     "requests-mock>=1.11.0",
     "PyYAML>=6.0.1",
-    "click>=8.1.7"
+    "click>=8.1.7",
+    "pandas>=2.2.2"
 ]
 
 authors = [