diff --git a/Doc/library/unittest.rst b/Doc/library/unittest.rst
index 0a0993518efddc..952148c1e22bf8 100644
--- a/Doc/library/unittest.rst
+++ b/Doc/library/unittest.rst
@@ -215,6 +215,11 @@ Command-line options
 
    See `Signal Handling`_ for the functions that provide this functionality.
 
+.. cmdoption:: --debug
+
+   Run test cases in :meth:`~TestCase.debug` mode.
+   This is useful for post-mortem debugging via :mod:`pdb`.
+
 .. cmdoption:: -f, --failfast
 
    Stop the test run on the first error or failure.
@@ -248,6 +253,9 @@ Command-line options
 .. versionadded:: 3.7
    The command-line option ``-k``.
 
+.. versionadded:: 3.10
+   The command-line option ``--debug``.
+
 The command line can also be used for test discovery, for running all of the
 tests in a project or just a subset.
 
diff --git a/Lib/unittest/main.py b/Lib/unittest/main.py
index e62469aa2a170f..55bf6caa52832c 100644
--- a/Lib/unittest/main.py
+++ b/Lib/unittest/main.py
@@ -65,7 +65,8 @@ class TestProgram(object):
     def __init__(self, module='__main__', defaultTest=None, argv=None,
                     testRunner=None, testLoader=loader.defaultTestLoader,
                     exit=True, verbosity=1, failfast=None, catchbreak=None,
-                    buffer=None, warnings=None, *, tb_locals=False):
+                    buffer=None, warnings=None, *, tb_locals=False,
+                    debug=False):
         if isinstance(module, str):
             self.module = __import__(module)
             for part in module.split('.')[1:]:
@@ -81,6 +82,7 @@ def __init__(self, module='__main__', defaultTest=None, argv=None,
         self.verbosity = verbosity
         self.buffer = buffer
         self.tb_locals = tb_locals
+        self.debug = debug
         if warnings is None and not sys.warnoptions:
             # even if DeprecationWarnings are ignored by default
             # print them anyway unless other warnings settings are
@@ -175,6 +177,8 @@ def _getParentArgParser(self):
         parser.add_argument('--locals', dest='tb_locals',
                             action='store_true',
                             help='Show local variables in tracebacks')
+        parser.add_argument('--debug', action='store_true',
+                            help='Run the given tests in debug mode')
         if self.failfast is None:
             parser.add_argument('-f', '--failfast', dest='failfast',
                                 action='store_true',
@@ -268,8 +272,11 @@ def runTests(self):
         else:
             # it is assumed to be a TestRunner instance
             testRunner = self.testRunner
-        self.result = testRunner.run(self.test)
+        if self.debug:
+            testRunner.debug(self.test)
+        else:
+            self.result = testRunner.run(self.test)
         if self.exit:
-            sys.exit(not self.result.wasSuccessful())
+            sys.exit(not (self.debug or self.result.wasSuccessful()))
 
 main = TestProgram
diff --git a/Lib/unittest/runner.py b/Lib/unittest/runner.py
index 45e7e4c0458d4c..1a6869eb324a82 100644
--- a/Lib/unittest/runner.py
+++ b/Lib/unittest/runner.py
@@ -10,6 +10,12 @@
 __unittest = True
 
 
+class TestRunner:
+    def debug(self, test):
+        """Run the given test case or test suite in debug mode."""
+        test.debug()
+
+
 class _WritelnDecorator(object):
     """Used to decorate file-like objects with a handy 'writeln' method"""
     def __init__(self,stream):
@@ -117,7 +123,7 @@ def printErrorList(self, flavour, errors):
             self.stream.writeln("%s" % err)
 
 
-class TextTestRunner(object):
+class TextTestRunner(TestRunner):
     """A test runner class that displays results in textual form.
 
     It prints out the names of tests as they are run, errors as they
diff --git a/Lib/unittest/test/test_break.py b/Lib/unittest/test/test_break.py
index eebd2b610ce11f..deb9dbe43d7424 100644
--- a/Lib/unittest/test/test_break.py
+++ b/Lib/unittest/test/test_break.py
@@ -207,6 +207,7 @@ def __init__(self, catchbreak):
                 self.failfast = failfast
                 self.catchbreak = catchbreak
                 self.tb_locals = False
+                self.debug = False
                 self.testRunner = FakeRunner
                 self.test = test
                 self.result = None
diff --git a/Lib/unittest/test/test_program.py b/Lib/unittest/test/test_program.py
index eef82ff937ab7c..ce20106b0078b4 100644
--- a/Lib/unittest/test/test_program.py
+++ b/Lib/unittest/test/test_program.py
@@ -129,6 +129,37 @@ def test_ExitAsDefault(self):
             testRunner=unittest.TextTestRunner(stream=io.StringIO()),
             testLoader=self.FooBarLoader())
 
+    class TestRaise(unittest.TestCase):
+        class Error(Exception):
+            pass
+        def test_raise(self):
+            raise self.Error
+
+    class TestRaiseLoader(unittest.TestLoader):
+        def loadTestsFromModule(self, module):
+            return self.suiteClass(
+                [self.loadTestsFromTestCase(Test_TestProgram.TestRaise)])
+
+        def loadTestsFromNames(self, names, module):
+            return self.suiteClass(
+                [self.loadTestsFromTestCase(Test_TestProgram.TestRaise)])
+
+    def test_debug(self):
+        self.assertRaises(
+            self.TestRaise.Error,
+            unittest.main,
+            argv=["TestRaise", "--debug"],
+            testRunner=unittest.TextTestRunner(stream=io.StringIO()),
+            testLoader=self.TestRaiseLoader())
+
+    def test_no_debug(self):
+        self.assertRaises(
+            SystemExit,
+            unittest.main,
+            argv=["TestRaise"],
+            testRunner=unittest.TextTestRunner(stream=io.StringIO()),
+            testLoader=self.TestRaiseLoader())
+
 
 class InitialisableProgram(unittest.TestProgram):
     exit = False
@@ -136,6 +167,7 @@ class InitialisableProgram(unittest.TestProgram):
     verbosity = 1
     defaultTest = None
     tb_locals = False
+    debug = False
     testRunner = None
     testLoader = unittest.defaultTestLoader
     module = '__main__'
@@ -289,6 +321,12 @@ def test_locals(self):
                                                'verbosity': 1,
                                                'warnings': None})
 
+    def test_debug(self):
+        program = self.program
+        program.testRunner = FakeRunner
+        program.parseArgs([None, '--debug'])
+        self.assertTrue(program.debug)
+
     def testRunTestsOldRunnerClass(self):
         program = self.program
 
diff --git a/Misc/NEWS.d/next/Library/2020-12-24-02-26-25.bpo-42722.ZNAp9W.rst b/Misc/NEWS.d/next/Library/2020-12-24-02-26-25.bpo-42722.ZNAp9W.rst
new file mode 100644
index 00000000000000..02b7dd623a8e0e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-12-24-02-26-25.bpo-42722.ZNAp9W.rst
@@ -0,0 +1 @@
+Added `--debug` command line option to :mod:`unittest`.