@@ -38,6 +38,9 @@ Git executable and safety
   suppresses configured signing by default; signing, verification, and editor
   options require the same opt-in.
 * The raw ``repo.git`` interface remains available for direct Git commands.
+  Global ``-C`` options select the requested checkout without the repository
+  locations automatically supplied by ``Repo`` overriding it. Explicit
+  environment overrides retain Git's precedence over ``-C``.
   Existing explicit unsafe-option and unsafe-protocol opt-ins remain independent.
   They do not permit argument or stdin-record injection, or reordering command
   options past the library's safety flags.
 
@@ -616,6 +616,7 @@ class Git:
         "_git_options",
         "_persistent_git_options",
         "_environment",
+        "_repository_environment",
         "_repo",
     )
 
@@ -1164,6 +1165,7 @@ def __init__(self, working_dir: Union[None, PathLike] = None) -> None:
 
         # Extra environment variables to pass to git commands
         self._environment: Dict[str, Optional[str]] = {}
+        self._repository_environment: Dict[str, Optional[str]] = {}
         self._repo: Any = None  # Weak reference; the Repo owns native resources.
 
         # Cached version slots
@@ -1535,7 +1537,11 @@ def execute(
         # just to be sure.
         environment["LANGUAGE"] = "C"
         environment["LC_ALL"] = "C"
-        environment.update(self._environment)
+        redirected = subprocess_kwargs.pop("_repository_redirected", False)
+        automatic = self._repository_environment if redirected else {}
+        environment.update(
+            {key: value for key, value in self._environment.items() if key not in automatic or value != automatic[key]}
+        )
         if inline_env is not None:
             environment.update(inline_env)
         # Internal or per-call None overrides remove inherited variables.
@@ -1725,6 +1731,7 @@ def update_environment(self, **kwargs: Any) -> Dict[str, Union[str, None]]:
         """
         old_env = {}
         for key, value in kwargs.items():
+            self._repository_environment.pop(key, None)
             # Set value if it is None.
             if value is not None:
                 old_env[key] = self._environment.get(key)
@@ -1748,11 +1755,13 @@ def custom_environment(self, **kwargs: Any) -> Iterator[None]:
         :param kwargs:
             See :meth:`update_environment`.
         """
+        automatic = {key: self._repository_environment[key] for key in kwargs if key in self._repository_environment}
         old_env = self.update_environment(**kwargs)
         try:
             yield
         finally:
             self.update_environment(**old_env)
+            self._repository_environment.update(automatic)
 
     def transform_kwarg(self, name: str, value: Any, split_single_char_options: bool) -> List[str]:
         if len(name) == 1:
@@ -1907,6 +1916,11 @@ def _call_process(
         call.extend(self._git_options)
         self._git_options = ()
 
+        # Only global options redirect discovery. A subcommand operand named
+        # -C must not drop the repository locations supplied by Repo.
+        if any(option == "-C" for option in call[1:]):
+            exec_kwargs["_repository_redirected"] = True
+
         call.extend(safe_git_options)
 
         call.append(dashify(method))
 
@@ -447,8 +447,12 @@ def __init__(
         self.git = self.GitCommandWrapperType(self.working_dir)
         self.git._repo = weakref.ref(self)
         self.git._environment.update(GIT_DIR=git_dir, **environment)
+        if git_dir_env is None:
+            self.git._repository_environment["GIT_DIR"] = git_dir
         if self._working_tree_dir is not None:
             self.git.update_environment(GIT_WORK_TREE=os.fspath(self._working_tree_dir))
+            if "GIT_WORK_TREE" not in environment:
+                self.git._repository_environment["GIT_WORK_TREE"] = os.fspath(self._working_tree_dir)
         if native is not NotImplemented:
             self._gix_repository = native
             self._empty_tree_hexsha = str(native.empty_tree().id)
 
@@ -31,3 +31,35 @@ def test_index_entries_readers_retain_pending_and_published_snapshots(object_for
         index.write()
         assert repo.index.entries == pending
         assert entries[("tracked", 0)].binsha == repo.head.commit.tree["tracked"].binsha
+
+
+@pytest.mark.parametrize("object_format", ["sha1", "sha256"])
+@pytest.mark.parametrize("ref_format", ["files", "reftable"])
+def test_git_directory_option_selects_the_requested_worktree(object_format, ref_format):
+    with fixture_repo("downstream-worktree.sh", object_format, ref_format, write=True) as repo:
+        root = Path(repo.working_tree_dir).parent
+        linked = root / "linked"
+        original_index = Path(repo.index.path).read_bytes()
+        assert not (linked / "tracked").exists()
+        process = repo.git(C=str(linked)).checkout("--force", as_process=True)
+        process.wait()
+        assert (linked / "tracked").read_text() == "original"
+        assert Path(repo.working_tree_dir, "tracked").read_text() == "unchanged"
+        assert Path(repo.index.path).read_bytes() == original_index
+        assert repo.git(C=str(linked)).rev_parse("--show-toplevel") == str(linked)
+        assert repo.git(C=str(root / "other")).show("HEAD:tracked") == "other"
+        repo.git.set_persistent_git_options(C=str(linked))
+        assert repo.git.rev_parse("--show-toplevel") == str(linked)
+        repo.git.set_persistent_git_options()
+        assert repo.git.rev_parse("--show-toplevel") == repo.working_tree_dir
+
+
+def test_git_directory_option_retains_explicit_environment():
+    with fixture_repo("downstream-worktree.sh", "sha1", "files", write=True) as repo:
+        root = Path(repo.working_tree_dir).parent
+        other = root / "other"
+        with repo.git.custom_environment(GIT_DIR=repo.git_dir, GIT_WORK_TREE=repo.working_tree_dir):
+            assert repo.git(C=str(other)).show("HEAD:tracked") == "original"
+        assert repo.git(C=str(other)).show("HEAD:tracked") == "other"
+        assert repo.git(C=str(other)).show("HEAD:tracked", env={"GIT_DIR": repo.git_dir}) == "original"
+
@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -eu
+git init -q --object-format="$1" --ref-format="$2" repo
+cd repo
+printf original > tracked
+git add tracked
+git commit -qm initial
+git worktree add -q --no-checkout -b linked ../linked HEAD
+printf unchanged > tracked
+git init -q ../other
+cd ../other
+printf other > tracked
+git add tracked
+git commit -qm other