diff --git a/src/pip/_internal/cli/req_command.py b/src/pip/_internal/cli/req_command.py
index 4b1f3365c..3ce4f1eec 100644
--- a/src/pip/_internal/cli/req_command.py
+++ b/src/pip/_internal/cli/req_command.py
@@ -34,6 +34,7 @@ from pip._internal.req.req_file import parse_requirements
 from pip._internal.req.req_install import InstallRequirement
 from pip._internal.resolution.base import BaseResolver
 from pip._internal.self_outdated_check import pip_self_version_check
+from pip._internal.utils.misc import merge_config_settings
 from pip._internal.utils.temp_dir import (
     TempDirectory,
     TempDirectoryTypeRegistry,
@@ -434,14 +435,21 @@ class RequirementCommand(IndexGroupCommand):
             for parsed_req in parse_requirements(
                 filename, finder=finder, options=options, session=session
             ):
+                config_settings = (
+                    parsed_req.options.get("config_settings")
+                    if parsed_req.options
+                    else None
+                )
+                if config_settings and options.config_settings:
+                    config_settings = merge_config_settings(
+                        config_settings, options.config_settings
+                    )
                 req_to_add = install_req_from_parsed_requirement(
                     parsed_req,
                     isolated=options.isolated_mode,
                     use_pep517=options.use_pep517,
                     user_supplied=True,
-                    config_settings=parsed_req.options.get("config_settings")
-                    if parsed_req.options
-                    else None,
+                    config_settings=config_settings,
                 )
                 requirements.append(req_to_add)
 
diff --git a/src/pip/_internal/utils/misc.py b/src/pip/_internal/utils/misc.py
index baa1ba7ea..63a8c3e1a 100644
--- a/src/pip/_internal/utils/misc.py
+++ b/src/pip/_internal/utils/misc.py
@@ -14,6 +14,8 @@ import stat
 import sys
 import sysconfig
 import urllib.parse
+from collections import defaultdict
+from collections.abc import Iterable
 from io import StringIO
 from itertools import filterfalse, tee, zip_longest
 from types import TracebackType
@@ -24,7 +26,6 @@ from typing import (
     ContextManager,
     Dict,
     Generator,
-    Iterable,
     Iterator,
     List,
     Optional,
@@ -32,6 +33,7 @@ from typing import (
     Tuple,
     Type,
     TypeVar,
+    Union,
     cast,
 )
 
@@ -60,6 +62,7 @@ __all__ = [
     "remove_auth_from_url",
     "check_externally_managed",
     "ConfiguredBuildBackendHookCaller",
+    "merge_config_settings",
 ]
 
 logger = logging.getLogger(__name__)
@@ -737,3 +740,17 @@ class ConfiguredBuildBackendHookCaller(BuildBackendHookCaller):
             config_settings=cs,
             _allow_fallback=_allow_fallback,
         )
+
+
+def merge_config_settings(
+    reqs_settings: Dict[str, Union[str, List[str]]],
+    cli_settings: Dict[str, Union[str, List[str]]],
+) -> Dict[str, Union[str, List[str]]]:
+    dd = defaultdict(list)
+    for d in (reqs_settings, cli_settings):
+        for k, v in d.items():
+            if isinstance(v, list):
+                dd[k].extend(v)
+            else:
+                dd[k].append(v)
+    return dict(dd)
diff --git a/tests/functional/test_config_settings.py b/tests/functional/test_config_settings.py
index c6a842213..0142fcb22 100644
--- a/tests/functional/test_config_settings.py
+++ b/tests/functional/test_config_settings.py
@@ -181,3 +181,30 @@ def test_install_config_reqs(script: PipTestEnvironment) -> None:
     config = script.site_packages_path / "config.json"
     with open(config, "rb") as f:
         assert json.load(f) == {"--build-option": ["--cffi", "--avx2"]}
+
+
+def test_merge_cli_reqs_config_settings(script: PipTestEnvironment) -> None:
+    _, _, project_dir = make_project(script.scratch_path)
+    a_sdist = create_basic_sdist_for_package(
+        script,
+        "foo",
+        "1.0",
+        {"pyproject.toml": PYPROJECT_TOML, "backend/dummy_backend.py": BACKEND_SRC},
+    )
+    script.scratch_path.joinpath("reqs.txt").write_text(
+        'foo --config-settings "FOO=HELLO" --config-settings "FOO=BAR"'
+    )
+    script.pip(
+        "install",
+        "--no-index",
+        "-f",
+        str(a_sdist.parent),
+        "-r",
+        "reqs.txt",
+        "--config-settings",
+        "FOO=FOOBAR",
+    )
+    script.assert_installed(foo="1.0")
+    config = script.site_packages_path / "config.json"
+    with open(config, "rb") as f:
+        assert json.load(f) == {"FOO": ["HELLO", "BAR", "FOOBAR"]}