diff --git a/.chronus/changes/preserve-pyproject-fields-2026-06-15.md b/.chronus/changes/preserve-pyproject-fields-2026-06-15.md
new file mode 100644
index 00000000000..3642556247f
--- /dev/null
+++ b/.chronus/changes/preserve-pyproject-fields-2026-06-15.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Preserve manually customized `description`, `classifiers`, and `[project.urls]` fields in an existing `pyproject.toml` instead of overwriting them on regeneration.
diff --git a/packages/http-client-python/generator/pygen/codegen/serializers/general_serializer.py b/packages/http-client-python/generator/pygen/codegen/serializers/general_serializer.py
index 6c022c9259b..d94282ac662 100644
--- a/packages/http-client-python/generator/pygen/codegen/serializers/general_serializer.py
+++ b/packages/http-client-python/generator/pygen/codegen/serializers/general_serializer.py
@@ -85,6 +85,13 @@ def external_lib_version_map(self, file_content: str, additional_version_map: di
 
         # Process dependencies
         if "project" in loaded_pyproject_toml:
+            project = loaded_pyproject_toml["project"]
+
+            # Keep manually customized project fields the emitter would otherwise overwrite.
+            for field in ("description", "classifiers", "urls"):
+                if field in project:
+                    result["KEEP_FIELDS"][f"project.{field}"] = project[field]
+
             # Handle main dependencies
             if "dependencies" in loaded_pyproject_toml["project"]:
                 kept_deps = []
diff --git a/packages/http-client-python/generator/pygen/codegen/templates/packaging_templates/pyproject.toml.jinja2 b/packages/http-client-python/generator/pygen/codegen/templates/packaging_templates/pyproject.toml.jinja2
index 4a012849501..851cc641b3a 100644
--- a/packages/http-client-python/generator/pygen/codegen/templates/packaging_templates/pyproject.toml.jinja2
+++ b/packages/http-client-python/generator/pygen/codegen/templates/packaging_templates/pyproject.toml.jinja2
@@ -14,12 +14,21 @@ name = "{{ options.get('package-name')|lower }}"
 authors = [
   { name = "{{ code_model.company_name }}"{% if code_model.is_azure_flavor %}, email = "azpysdkhelp@microsoft.com"{% endif %} },
 ]
-{% if options.get("azure-arm") %}
+{% if KEEP_FIELDS and KEEP_FIELDS.get('project.description') %}
+description = {{ KEEP_FIELDS.get('project.description')|tojson }}
+{% elif options.get("azure-arm") %}
 description = "Microsoft Azure {{ options.get('package-pprint-name') }} Client Library for Python"
 {% else %}
 description = "{{ code_model.company_name }} {% if code_model.is_azure_flavor and not options.get('package-pprint-name').startswith('Azure ') %}Azure {% endif %}{{ options.get('package-pprint-name') }} Client Library for Python"
 {% endif %}
 license = "MIT"
+{% if KEEP_FIELDS and KEEP_FIELDS.get('project.classifiers') %}
+classifiers = [
+    {% for classifier in KEEP_FIELDS.get('project.classifiers') %}
+    {{ classifier|tojson }},
+    {% endfor %}
+]
+{% else %}
 classifiers = [
     "Development Status :: {{ dev_status }}",
     "Programming Language :: Python",
@@ -29,10 +38,15 @@ classifiers = [
     "Programming Language :: Python :: 3.{{ version }}",
     {% endfor %}
 ]
+{% endif %}
 requires-python = ">={{ MIN_PYTHON_VERSION }}"
 {% else %}
+{% if KEEP_FIELDS and KEEP_FIELDS.get('project.description') %}
+description = {{ KEEP_FIELDS.get('project.description')|tojson }}
+{% else %}
 description = "{{ options.get('package-name') }}"
 {% endif %}
+{% endif %}
 {% if code_model.is_azure_flavor %}
 keywords = ["azure", "azure sdk"]
 {% endif %}
@@ -77,7 +91,13 @@ version = "{{ options.get("package-version", "unknown") }}"
 ]
 {% endfor %}
 {% endif %}
-{% if code_model.is_azure_flavor %}
+{% if KEEP_FIELDS and KEEP_FIELDS.get('project.urls') %}
+
+[project.urls]
+{% for key, val in KEEP_FIELDS.get('project.urls').items() %}
+{{ key }} = {{ val|tojson }}
+{% endfor %}
+{% elif code_model.is_azure_flavor %}
 
 [project.urls]
 repository = "https://github.com/Azure/azure-sdk-for-python"
diff --git a/packages/http-client-python/tests/unit/test_pyproject_keep_fields.py b/packages/http-client-python/tests/unit/test_pyproject_keep_fields.py
new file mode 100644
index 00000000000..b52a8a4f4a8
--- /dev/null
+++ b/packages/http-client-python/tests/unit/test_pyproject_keep_fields.py
@@ -0,0 +1,72 @@
+# -------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for
+# license information.
+# --------------------------------------------------------------------------
+"""Unit tests for preserving manually customized pyproject.toml fields.
+
+The emitter regenerates pyproject.toml on every emit. Manual edits to fields
+the emitter doesn't own (description, classifiers, project URLs) must be
+preserved so they are not clobbered (see GitHub issue #10311).
+"""
+from pygen.codegen.serializers.general_serializer import GeneralSerializer
+
+
+def _keep_fields(file_content: str) -> dict:
+    # external_lib_version_map only relies on module-level helpers, not on
+    # instance state, so we can bypass __init__ for a focused unit test.
+    serializer = GeneralSerializer.__new__(GeneralSerializer)
+    return serializer.external_lib_version_map(file_content, {})["KEEP_FIELDS"]
+
+
+def test_preserve_description():
+    content = """
+[project]
+name = "azure-ai-sample"
+description = "Microsoft Azure AI Sample Client Library for Python"
+"""
+    keep_fields = _keep_fields(content)
+    assert keep_fields["project.description"] == "Microsoft Azure AI Sample Client Library for Python"
+
+
+def test_preserve_classifiers():
+    content = """
+[project]
+name = "azure-ai-sample"
+classifiers = [
+    "Development Status :: 5 - Production/Stable",
+    "Programming Language :: Python :: 3.13",
+    "Programming Language :: Python :: 3.14",
+]
+"""
+    keep_fields = _keep_fields(content)
+    assert "Programming Language :: Python :: 3.14" in keep_fields["project.classifiers"]
+
+
+def test_preserve_project_urls():
+    content = """
+[project]
+name = "azure-ai-sample"
+
+[project.urls]
+repository = "https://github.com/Azure/azure-sdk-for-python-custom"
+documentation = "https://aka.ms/custom-docs"
+"""
+    keep_fields = _keep_fields(content)
+    assert keep_fields["project.urls"]["repository"] == "https://github.com/Azure/azure-sdk-for-python-custom"
+    assert keep_fields["project.urls"]["documentation"] == "https://aka.ms/custom-docs"
+
+
+def test_missing_fields_not_kept():
+    content = """
+[project]
+name = "azure-ai-sample"
+"""
+    keep_fields = _keep_fields(content)
+    assert "project.description" not in keep_fields
+    assert "project.classifiers" not in keep_fields
+    assert "project.urls" not in keep_fields
+
+
+def test_invalid_toml_returns_empty():
+    assert _keep_fields("this is : not valid = toml [[[") == {}