--- a/python/mach_commands.py
+++ b/python/mach_commands.py
@@ -12,16 +12,17 @@ import os
 from concurrent.futures import (
     ThreadPoolExecutor,
     as_completed,
     thread,
 )
 
 import mozinfo
 from manifestparser import TestManifest
+from manifestparser import filters as mpf
 
 from mozbuild.base import (
     MachCommandBase,
 )
 
 from mach.decorators import (
     CommandArgument,
     CommandProvider,
@@ -60,16 +61,20 @@ class MachCommands(MachCommandBase):
         default=False,
         action='store_true',
         help=('Collect all tests under given path instead of default '
               'test resolution. Supports pytest-style tests.'))
     @CommandArgument('-j', '--jobs',
         default=1,
         type=int,
         help='Number of concurrent jobs to run. Default is 1.')
+    @CommandArgument('--subsuite',
+        default=None,
+        help=('Python subsuite to run. If not specified, all subsuites are run. '
+             'Use the string `default` to only run tests without a subsuite.'))
     @CommandArgument('tests', nargs='*',
         metavar='TEST',
         help=('Tests to run. Each test can be a single file or a directory. '
               'Default test resolution relies on PYTHON_UNITTEST_MANIFESTS.'))
     def python_test(self,
                     tests=[],
                     test_objects=None,
                     subsuite=None,
@@ -128,17 +133,24 @@ class MachCommands(MachCommandBase):
             message = 'TEST-UNEXPECTED-FAIL | No tests collected'
             if not path_only:
                 message += ' (Not in PYTHON_UNITTEST_MANIFESTS? Try --path-only?)'
             self.log(logging.WARN, 'python-test', {}, message)
             return 1
 
         mp = TestManifest()
         mp.tests.extend(test_objects)
-        tests = mp.active_tests(disabled=False, **mozinfo.info)
+
+        filters = []
+        if subsuite == 'default':
+            filters.append(mpf.subsuite(None))
+        elif subsuite:
+            filters.append(mpf.subsuite(subsuite))
+
+        tests = mp.active_tests(filters=filters, disabled=False, **mozinfo.info)
 
         self.jobs = jobs
         self.terminate = False
         self.verbose = verbose
 
         return_code = 0
         with ThreadPoolExecutor(max_workers=self.jobs) as executor:
             futures = [executor.submit(self._run_python_test, test['path'])