diff --git a/src/cq_cli/main.py b/src/cq_cli/main.py
index 914fbd8..64377a3 100755
--- a/src/cq_cli/main.py
+++ b/src/cq_cli/main.py
@@ -20,13 +20,15 @@
 from cq_cli.cqcodecs import loader
 
 
-def build_and_parse(script_str, params, errfile):
+def build_and_parse(script_str, params, errfile, expression):
     """
     Uses CQGI to parse and build a script, substituting in parameters if any were supplied.
     """
     # We need to do a broad try/catch to let the user know if something higher-level fails
     try:
         # Do the CQGI handling of the script here and, if successful, pass the build result to the codec
+        if expression != None:
+            script_str += "\nshow_object({expr})".format(expr=expression)
         cqModel = cqgi.parse(script_str)
         build_result = cqModel.build(params)
 
@@ -181,6 +183,10 @@ def main():
         "--validate",
         help="Setting to true forces the CLI to only parse and validate the script and not produce converted output.",
     )
+    parser.add_argument(
+        "--expression",
+        help="A python expression (such as `my_shape(x=5)`) to evaluate and render. This allows rendering different models/parts from the same python file.",
+    )
 
     args = parser.parse_args()
 
@@ -223,7 +229,7 @@ def main():
         # Set the PYTHONPATH variable to the current directory to allow module loading
         set_pythonpath_for_infile(args.infile)
 
-        build_result = build_and_parse(script_str, params, errfile)
+        build_result = build_and_parse(script_str, params, errfile, args.expression)
 
         # Double-check that the build was a success
         if build_result != None and build_result.success:
@@ -424,7 +430,7 @@ def main():
     #
     build_result = None
     try:
-        build_result = build_and_parse(script_str, params, errfile)
+        build_result = build_and_parse(script_str, params, errfile, args.expression)
 
         # If None was returned, it means the build failed and the exception has already been reported
         if build_result == None:
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 75c1a6d..fe77199 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -407,3 +407,52 @@ def test_exit_codes():
 
     # Make sure that we got exit code 100 for a failed model build
     assert exitcode == 100
+
+
+def test_expression_argument():
+    """
+    Tests the CLI with the the expression argument.
+    """
+    test_file = helpers.get_test_file_location("no_toplevel_objects.py")
+
+    # Get a temporary output file location
+    temp_dir = tempfile.gettempdir()
+    temp_file = os.path.join(temp_dir, "temp_test_10.step")
+
+    # Run cq-cli with --expression "cube()"
+    command = [
+        "python",
+        "src/cq_cli/main.py",
+        "--codec",
+        "step",
+        "--infile",
+        test_file,
+        "--outfile",
+        temp_file,
+        "--expression",
+        "cube()",
+    ]
+    out, err, exitcode = helpers.cli_call(command)
+
+    # Read the STEP output back from the outfile
+    with open(temp_file, "r") as file:
+        step_str = file.read()
+
+    assert step_str.startswith("ISO-10303-21;")
+
+    # Run cq-cli on the same model file, but don't specify an --expression. This
+    # should fail because the file contains no top-level show_object() calls.
+    command = [
+        "python",
+        "src/cq_cli/main.py",
+        "--codec",
+        "step",
+        "--infile",
+        test_file,
+        "--outfile",
+        temp_file,
+    ]
+    out, err, exitcode = helpers.cli_call(command)
+
+    # cq-cli invocation should fail
+    assert exitcode == 200
diff --git a/tests/testdata/no_toplevel_objects.py b/tests/testdata/no_toplevel_objects.py
new file mode 100644
index 0000000..531e1fd
--- /dev/null
+++ b/tests/testdata/no_toplevel_objects.py
@@ -0,0 +1,8 @@
+import cadquery as cq
+
+# This test file contains a method for creating a shape, but does not contain
+# any top-level `show_object()` calls.
+
+
+def cube():
+    return cq.Workplane().box(1, 1, 1)