diff --git a/homeassistant/components/portainer/diagnostics.py b/homeassistant/components/portainer/diagnostics.py
new file mode 100644
index 00000000000..f95b75b294c
--- /dev/null
+++ b/homeassistant/components/portainer/diagnostics.py
@@ -0,0 +1,55 @@
+"""Diagnostics for the Portainer integration."""
+
+from __future__ import annotations
+
+from typing import Any
+
+from homeassistant.components.diagnostics import async_redact_data
+from homeassistant.const import CONF_API_TOKEN
+from homeassistant.core import HomeAssistant
+
+from . import PortainerConfigEntry
+from .coordinator import PortainerCoordinator
+
+TO_REDACT = [CONF_API_TOKEN]
+
+
+def _serialize_coordinator(coordinator: PortainerCoordinator) -> dict[str, Any]:
+    """Serialize coordinator data into a JSON-safe structure."""
+
+    serialized_endpoints: list[dict[str, Any]] = []
+    for endpoint_id, endpoint_data in coordinator.data.items():
+        serialized_endpoints.append(
+            {
+                "id": endpoint_id,
+                "name": endpoint_data.name,
+                "endpoint": {
+                    "status": endpoint_data.endpoint.status,
+                    "url": endpoint_data.endpoint.url,
+                    "public_url": endpoint_data.endpoint.public_url,
+                },
+                "containers": [
+                    {
+                        "id": container.id,
+                        "names": list(container.names or []),
+                        "image": container.image,
+                        "state": container.state,
+                        "status": container.status,
+                    }
+                    for container in endpoint_data.containers.values()
+                ],
+            }
+        )
+
+    return {"endpoints": serialized_endpoints}
+
+
+async def async_get_config_entry_diagnostics(
+    hass: HomeAssistant, config_entry: PortainerConfigEntry
+) -> dict[str, Any]:
+    """Return diagnostics for a Portainer config entry."""
+
+    return {
+        "config_entry": async_redact_data(config_entry.as_dict(), TO_REDACT),
+        "coordinator": _serialize_coordinator(config_entry.runtime_data),
+    }
diff --git a/homeassistant/components/portainer/quality_scale.yaml b/homeassistant/components/portainer/quality_scale.yaml
index d26f0087d87..d0f95bb8591 100644
--- a/homeassistant/components/portainer/quality_scale.yaml
+++ b/homeassistant/components/portainer/quality_scale.yaml
@@ -44,7 +44,7 @@ rules:
   test-coverage: done
   # Gold
   devices: done
-  diagnostics: todo
+  diagnostics: done
   discovery-update-info:
     status: exempt
     comment: |
diff --git a/tests/components/portainer/snapshots/test_diagnostics.ambr b/tests/components/portainer/snapshots/test_diagnostics.ambr
new file mode 100644
index 00000000000..8ce3040f4dc
--- /dev/null
+++ b/tests/components/portainer/snapshots/test_diagnostics.ambr
@@ -0,0 +1,88 @@
+# serializer version: 1
+# name: test_get_config_entry_diagnostics
+  dict({
+    'config_entry': dict({
+      'data': dict({
+        'api_token': '**REDACTED**',
+        'url': 'https://127.0.0.1:9000/',
+        'verify_ssl': True,
+      }),
+      'disabled_by': None,
+      'discovery_keys': dict({
+      }),
+      'domain': 'portainer',
+      'entry_id': 'portainer_test_entry_123',
+      'minor_version': 1,
+      'options': dict({
+      }),
+      'pref_disable_new_entities': False,
+      'pref_disable_polling': False,
+      'source': 'user',
+      'subentries': list([
+      ]),
+      'title': 'Portainer test',
+      'unique_id': None,
+      'version': 2,
+    }),
+    'coordinator': dict({
+      'endpoints': list([
+        dict({
+          'containers': list([
+            dict({
+              'id': 'aa86eacfb3b3ed4cd362c1e88fc89a53908ad05fb3a4103bca3f9b28292d14bf',
+              'image': 'docker.io/library/ubuntu:latest',
+              'names': list([
+                '/funny_chatelet',
+              ]),
+              'state': 'running',
+              'status': 'Up 4 days',
+            }),
+            dict({
+              'id': 'bb97facfb3b3ed4cd362c1e88fc89a53908ad05fb3a4103bca3f9b28292d14bf',
+              'image': 'docker.io/library/nginx:latest',
+              'names': list([
+                '/serene_banach',
+              ]),
+              'state': 'running',
+              'status': 'Up 2 days',
+            }),
+            dict({
+              'id': 'cc08facfb3b3ed4cd362c1e88fc89a53908ad05fb3a4103bca3f9b28292d14bf',
+              'image': 'docker.io/library/postgres:15',
+              'names': list([
+                '/stoic_turing',
+              ]),
+              'state': 'running',
+              'status': 'Up 1 day',
+            }),
+            dict({
+              'id': 'dd19facfb3b3ed4cd362c1e88fc89a53908ad05fb3a4103bca3f9b28292d14bf',
+              'image': 'docker.io/library/redis:7',
+              'names': list([
+                '/focused_einstein',
+              ]),
+              'state': 'running',
+              'status': 'Up 12 hours',
+            }),
+            dict({
+              'id': 'ee20facfb3b3ed4cd362c1e88fc89a53908ad05fb3a4103bca3f9b28292d14bf',
+              'image': 'docker.io/library/python:3.13-slim',
+              'names': list([
+                '/practical_morse',
+              ]),
+              'state': 'running',
+              'status': 'Up 6 hours',
+            }),
+          ]),
+          'endpoint': dict({
+            'public_url': 'docker.mydomain.tld:2375',
+            'status': 1,
+            'url': 'docker.mydomain.tld:2375',
+          }),
+          'id': 1,
+          'name': 'my-environment',
+        }),
+      ]),
+    }),
+  })
+# ---
diff --git a/tests/components/portainer/test_diagnostics.py b/tests/components/portainer/test_diagnostics.py
new file mode 100644
index 00000000000..882d80570a7
--- /dev/null
+++ b/tests/components/portainer/test_diagnostics.py
@@ -0,0 +1,32 @@
+"""Test the Portainer component diagnostics."""
+
+from unittest.mock import AsyncMock
+
+from syrupy.assertion import SnapshotAssertion
+from syrupy.filters import props
+
+from homeassistant.core import HomeAssistant
+
+from . import setup_integration
+
+from tests.common import MockConfigEntry
+from tests.components.diagnostics import get_diagnostics_for_config_entry
+from tests.typing import ClientSessionGenerator
+
+
+async def test_get_config_entry_diagnostics(
+    hass: HomeAssistant,
+    snapshot: SnapshotAssertion,
+    mock_portainer_client: AsyncMock,
+    mock_config_entry: MockConfigEntry,
+    hass_client: ClientSessionGenerator,
+) -> None:
+    """Test if get_config_entry_diagnostics returns the correct data."""
+    await setup_integration(hass, mock_config_entry)
+
+    diagnostics_entry = await get_diagnostics_for_config_entry(
+        hass, hass_client, mock_config_entry
+    )
+    assert diagnostics_entry == snapshot(
+        exclude=props("created_at", "modified_at"),
+    )