diff --git a/Lib/argparse.py b/Lib/argparse.py
index 49271a146c7282..024622bec17c3b 100644
--- a/Lib/argparse.py
+++ b/Lib/argparse.py
@@ -1924,6 +1924,9 @@ def parse_args(self, args=None, namespace=None):
         return args
 
     def parse_known_args(self, args=None, namespace=None):
+        return self._parse_known_args2(args, namespace, intermixed=False)
+
+    def _parse_known_args2(self, args, namespace, intermixed):
         if args is None:
             # args default to the system args
             args = _sys.argv[1:]
@@ -1950,18 +1953,18 @@ def parse_known_args(self, args=None, namespace=None):
         # parse the arguments and exit if there are any errors
         if self.exit_on_error:
             try:
-                namespace, args = self._parse_known_args(args, namespace)
+                namespace, args = self._parse_known_args(args, namespace, intermixed)
             except ArgumentError as err:
                 self.error(str(err))
         else:
-            namespace, args = self._parse_known_args(args, namespace)
+            namespace, args = self._parse_known_args(args, namespace, intermixed)
 
         if hasattr(namespace, _UNRECOGNIZED_ARGS_ATTR):
             args.extend(getattr(namespace, _UNRECOGNIZED_ARGS_ATTR))
             delattr(namespace, _UNRECOGNIZED_ARGS_ATTR)
         return namespace, args
 
-    def _parse_known_args(self, arg_strings, namespace):
+    def _parse_known_args(self, arg_strings, namespace, intermixed):
         # replace arg strings that are file references
         if self.fromfile_prefix_chars is not None:
             arg_strings = self._read_args_from_files(arg_strings)
@@ -2052,6 +2055,7 @@ def consume_optional(start_index):
                 # if we found no optional action, skip it
                 if action is None:
                     extras.append(arg_strings[start_index])
+                    extras_pattern.append('O')
                     return start_index + 1
 
                 # if there is an explicit argument, try to match the
@@ -2087,6 +2091,7 @@ def consume_optional(start_index):
                                 sep = ''
                         else:
                             extras.append(char + explicit_arg)
+                            extras_pattern.append('O')
                             stop = start_index + 1
                             break
                     # if the action expect exactly one argument, we've
@@ -2165,6 +2170,7 @@ def consume_positionals(start_index):
         # consume Positionals and Optionals alternately, until we have
         # passed the last option string
         extras = []
+        extras_pattern = []
         start_index = 0
         if option_string_indices:
             max_option_string_index = max(option_string_indices)
@@ -2178,7 +2184,7 @@ def consume_positionals(start_index):
                 if next_option_string_index in option_string_indices:
                     break
                 next_option_string_index += 1
-            if start_index != next_option_string_index:
+            if not intermixed and start_index != next_option_string_index:
                 positionals_end_index = consume_positionals(start_index)
 
                 # only try to parse the next optional if we didn't consume
@@ -2194,16 +2200,35 @@ def consume_positionals(start_index):
             if start_index not in option_string_indices:
                 strings = arg_strings[start_index:next_option_string_index]
                 extras.extend(strings)
+                extras_pattern.extend(arg_strings_pattern[start_index:next_option_string_index])
                 start_index = next_option_string_index
 
             # consume the next optional and any arguments for it
             start_index = consume_optional(start_index)
 
-        # consume any positionals following the last Optional
-        stop_index = consume_positionals(start_index)
+        if not intermixed:
+            # consume any positionals following the last Optional
+            stop_index = consume_positionals(start_index)
 
-        # if we didn't consume all the argument strings, there were extras
-        extras.extend(arg_strings[stop_index:])
+            # if we didn't consume all the argument strings, there were extras
+            extras.extend(arg_strings[stop_index:])
+        else:
+            extras.extend(arg_strings[start_index:])
+            extras_pattern.extend(arg_strings_pattern[start_index:])
+            extras_pattern = ''.join(extras_pattern)
+            assert len(extras_pattern) == len(extras)
+            # consume all positionals
+            arg_strings = [s for s, c in zip(extras, extras_pattern) if c != 'O']
+            arg_strings_pattern = extras_pattern.replace('O', '')
+            stop_index = consume_positionals(0)
+            # leave unknown optionals and non-consumed positionals in extras
+            for i, c in enumerate(extras_pattern):
+                if not stop_index:
+                    break
+                if c != 'O':
+                    stop_index -= 1
+                    extras[i] = None
+            extras = [s for s in extras if s is not None]
 
         # make sure all required actions were present and also convert
         # action defaults which were not given as arguments
@@ -2469,10 +2494,6 @@ def parse_known_intermixed_args(self, args=None, namespace=None):
         # are then parsed.  If the parser definition is incompatible with the
         # intermixed assumptions (e.g. use of REMAINDER, subparsers) a
         # TypeError is raised.
-        #
-        # positionals are 'deactivated' by setting nargs and default to
-        # SUPPRESS.  This blocks the addition of that positional to the
-        # namespace
 
         positionals = self._get_positional_actions()
         a = [action for action in positionals
@@ -2481,59 +2502,7 @@ def parse_known_intermixed_args(self, args=None, namespace=None):
             raise TypeError('parse_intermixed_args: positional arg'
                             ' with nargs=%s'%a[0].nargs)
 
-        if [action.dest for group in self._mutually_exclusive_groups
-            for action in group._group_actions if action in positionals]:
-            raise TypeError('parse_intermixed_args: positional in'
-                            ' mutuallyExclusiveGroup')
-
-        try:
-            save_usage = self.usage
-            try:
-                if self.usage is None:
-                    # capture the full usage for use in error messages
-                    self.usage = self.format_usage()[7:]
-                for action in positionals:
-                    # deactivate positionals
-                    action.save_nargs = action.nargs
-                    # action.nargs = 0
-                    action.nargs = SUPPRESS
-                    action.save_default = action.default
-                    action.default = SUPPRESS
-                namespace, remaining_args = self.parse_known_args(args,
-                                                                  namespace)
-                for action in positionals:
-                    # remove the empty positional values from namespace
-                    if (hasattr(namespace, action.dest)
-                            and getattr(namespace, action.dest)==[]):
-                        from warnings import warn
-                        warn('Do not expect %s in %s' % (action.dest, namespace))
-                        delattr(namespace, action.dest)
-            finally:
-                # restore nargs and usage before exiting
-                for action in positionals:
-                    action.nargs = action.save_nargs
-                    action.default = action.save_default
-            optionals = self._get_optional_actions()
-            try:
-                # parse positionals.  optionals aren't normally required, but
-                # they could be, so make sure they aren't.
-                for action in optionals:
-                    action.save_required = action.required
-                    action.required = False
-                for group in self._mutually_exclusive_groups:
-                    group.save_required = group.required
-                    group.required = False
-                namespace, extras = self.parse_known_args(remaining_args,
-                                                          namespace)
-            finally:
-                # restore parser values before exiting
-                for action in optionals:
-                    action.required = action.save_required
-                for group in self._mutually_exclusive_groups:
-                    group.required = group.save_required
-        finally:
-            self.usage = save_usage
-        return namespace, extras
+        return self._parse_known_args2(args, namespace, intermixed=True)
 
     # ========================
     # Value conversion methods
diff --git a/Lib/test/test_argparse.py b/Lib/test/test_argparse.py
index 4fa669718abc50..4bd7a935b9b757 100644
--- a/Lib/test/test_argparse.py
+++ b/Lib/test/test_argparse.py
@@ -6412,12 +6412,23 @@ def test_basic(self):
         # cannot parse the '1,2,3'
         self.assertEqual(NS(bar='y', cmd='cmd', foo='x', rest=[1]), args)
         self.assertEqual(["2", "3"], extras)
+        args, extras = parser.parse_known_intermixed_args(argv)
+        self.assertEqual(NS(bar='y', cmd='cmd', foo='x', rest=[1, 2, 3]), args)
+        self.assertEqual([], extras)
 
+        # unknown optionals go into extras
+        argv = 'cmd --foo x --error 1 2 --bar y 3'.split()
+        args, extras = parser.parse_known_intermixed_args(argv)
+        self.assertEqual(NS(bar='y', cmd='cmd', foo='x', rest=[1, 2, 3]), args)
+        self.assertEqual(['--error'], extras)
         argv = 'cmd --foo x 1 --error 2 --bar y 3'.split()
         args, extras = parser.parse_known_intermixed_args(argv)
-        # unknown optionals go into extras
-        self.assertEqual(NS(bar='y', cmd='cmd', foo='x', rest=[1]), args)
-        self.assertEqual(['--error', '2', '3'], extras)
+        self.assertEqual(NS(bar='y', cmd='cmd', foo='x', rest=[1, 2, 3]), args)
+        self.assertEqual(['--error'], extras)
+        argv = 'cmd --foo x 1 2 --error --bar y 3'.split()
+        args, extras = parser.parse_known_intermixed_args(argv)
+        self.assertEqual(NS(bar='y', cmd='cmd', foo='x', rest=[1, 2, 3]), args)
+        self.assertEqual(['--error'], extras)
 
         # restores attributes that were temporarily changed
         self.assertIsNone(parser.usage)
@@ -6436,37 +6447,48 @@ def test_remainder(self):
             parser.parse_intermixed_args(argv)
         self.assertRegex(str(cm.exception), r'\.\.\.')
 
-    def test_exclusive(self):
-        # mutually exclusive group; intermixed works fine
-        parser = ErrorRaisingArgumentParser(prog='PROG')
+    def test_required_exclusive(self):
+        # required mutually exclusive group; intermixed works fine
+        parser = argparse.ArgumentParser(prog='PROG', exit_on_error=False)
         group = parser.add_mutually_exclusive_group(required=True)
         group.add_argument('--foo', action='store_true', help='FOO')
         group.add_argument('--spam', help='SPAM')
         parser.add_argument('badger', nargs='*', default='X', help='BADGER')
+        args = parser.parse_intermixed_args('--foo 1 2'.split())
+        self.assertEqual(NS(badger=['1', '2'], foo=True, spam=None), args)
         args = parser.parse_intermixed_args('1 --foo 2'.split())
         self.assertEqual(NS(badger=['1', '2'], foo=True, spam=None), args)
-        self.assertRaises(ArgumentParserError, parser.parse_intermixed_args, '1 2'.split())
+        self.assertRaisesRegex(argparse.ArgumentError,
+                'one of the arguments --foo --spam is required',
+                parser.parse_intermixed_args, '1 2'.split())
         self.assertEqual(group.required, True)
 
-    def test_exclusive_incompatible(self):
-        # mutually exclusive group including positional - fail
-        parser = ErrorRaisingArgumentParser(prog='PROG')
+    def test_required_exclusive_with_positional(self):
+        # required mutually exclusive group with positional argument
+        parser = argparse.ArgumentParser(prog='PROG', exit_on_error=False)
         group = parser.add_mutually_exclusive_group(required=True)
         group.add_argument('--foo', action='store_true', help='FOO')
         group.add_argument('--spam', help='SPAM')
         group.add_argument('badger', nargs='*', default='X', help='BADGER')
-        self.assertRaises(TypeError, parser.parse_intermixed_args, [])
+        args = parser.parse_intermixed_args(['--foo'])
+        self.assertEqual(NS(foo=True, spam=None, badger='X'), args)
+        args = parser.parse_intermixed_args(['a', 'b'])
+        self.assertEqual(NS(foo=False, spam=None, badger=['a', 'b']), args)
+        self.assertRaisesRegex(argparse.ArgumentError,
+                'one of the arguments --foo --spam badger is required',
+                parser.parse_intermixed_args, [])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                'argument badger: not allowed with argument --foo',
+                parser.parse_intermixed_args, ['--foo', 'a', 'b'])
+        self.assertRaisesRegex(argparse.ArgumentError,
+                'argument badger: not allowed with argument --foo',
+                parser.parse_intermixed_args, ['a', '--foo', 'b'])
         self.assertEqual(group.required, True)
 
     def test_invalid_args(self):
         parser = ErrorRaisingArgumentParser(prog='PROG')
         self.assertRaises(ArgumentParserError, parser.parse_intermixed_args, ['a'])
 
-        parser = ErrorRaisingArgumentParser(prog='PROG')
-        parser.add_argument('--foo', nargs="*")
-        parser.add_argument('foo')
-        with self.assertWarns(UserWarning):
-            parser.parse_intermixed_args(['hello', '--foo'])
 
 class TestIntermixedMessageContentError(TestCase):
     # case where Intermixed gives different error message
@@ -6485,7 +6507,7 @@ def test_missing_argument_name_in_message(self):
         with self.assertRaises(ArgumentParserError) as cm:
             parser.parse_intermixed_args([])
         msg = str(cm.exception)
-        self.assertNotRegex(msg, 'req_pos')
+        self.assertRegex(msg, 'req_pos')
         self.assertRegex(msg, 'req_opt')
 
 # ==========================
diff --git a/Misc/NEWS.d/next/Library/2024-10-22-13-28-00.gh-issue-125355.zssHm_.rst b/Misc/NEWS.d/next/Library/2024-10-22-13-28-00.gh-issue-125355.zssHm_.rst
new file mode 100644
index 00000000000000..fd67f697641d92
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-10-22-13-28-00.gh-issue-125355.zssHm_.rst
@@ -0,0 +1,7 @@
+Fix several bugs in :meth:`argparse.ArgumentParser.parse_intermixed_args`.
+
+* The parser no longer changes temporarily during parsing.
+* Default values are not processed twice.
+* Required mutually exclusive groups containing positional arguments are now supported.
+* The missing arguments report now includes the names of all required optional and positional arguments.
+* Unknown options can be intermixed with positional arguments in parse_known_intermixed_args().