diff --git a/news/9987.feature.rst b/news/9987.feature.rst
new file mode 100644
index 00000000000..0cf4516381d
--- /dev/null
+++ b/news/9987.feature.rst
@@ -0,0 +1 @@
+Include ``rustc`` version in pip's ``User-Agent``, when the system has ``rustc``.
diff --git a/src/pip/_internal/network/session.py b/src/pip/_internal/network/session.py
index 4af800f12fe..dca26374458 100644
--- a/src/pip/_internal/network/session.py
+++ b/src/pip/_internal/network/session.py
@@ -19,6 +19,8 @@
 import mimetypes
 import os
 import platform
+import shutil
+import subprocess
 import sys
 import urllib.parse
 import warnings
@@ -163,6 +165,21 @@ def user_agent():
     if setuptools_dist is not None:
         data["setuptools_version"] = str(setuptools_dist.version)
 
+    if shutil.which("rustc") is not None:
+        # If for any reason `rustc --version` fails, silently ignore it
+        try:
+            rustc_output = subprocess.check_output(
+                ["rustc", "--version"], stderr=subprocess.STDOUT, timeout=.5
+            )
+        except Exception:
+            pass
+        else:
+            if rustc_output.startswith(b"rustc "):
+                # The format of `rustc --version` is:
+                # `b'rustc 1.52.1 (9bc8c42bb 2021-05-09)\n'`
+                # We extract just the middle (1.52.1) part
+                data["rustc_version"] = rustc_output.split(b" ")[1].decode()
+
     # Use None rather than False so as not to give the impression that
     # pip knows it is not being run under CI.  Rather, it is a null or
     # inconclusive result.  Also, we include some value rather than no
diff --git a/tests/unit/test_req_file.py b/tests/unit/test_req_file.py
index 3c534c9ee01..be1e5815f2b 100644
--- a/tests/unit/test_req_file.py
+++ b/tests/unit/test_req_file.py
@@ -598,13 +598,16 @@ def make_var(name):
         with open(tmpdir.joinpath('req1.txt'), 'w') as fp:
             fp.write(template.format(*map(make_var, env_vars)))
 
+        # Construct the session outside the monkey-patch, since it access the
+        # env
+        session = PipSession()
         with patch('pip._internal.req.req_file.os.getenv') as getenv:
             getenv.side_effect = lambda n: env_vars[n]
 
             reqs = list(parse_reqfile(
                 tmpdir.joinpath('req1.txt'),
                 finder=finder,
-                session=PipSession()
+                session=session
             ))
 
         assert len(reqs) == 1, \
@@ -623,13 +626,16 @@ def test_expand_missing_env_variables(self, tmpdir, finder):
         with open(tmpdir.joinpath('req1.txt'), 'w') as fp:
             fp.write(req_url)
 
+        # Construct the session outside the monkey-patch, since it access the
+        # env
+        session = PipSession()
         with patch('pip._internal.req.req_file.os.getenv') as getenv:
             getenv.return_value = ''
 
             reqs = list(parse_reqfile(
                 tmpdir.joinpath('req1.txt'),
                 finder=finder,
-                session=PipSession()
+                session=session
             ))
 
             assert len(reqs) == 1, \