diff --git a/functest_requirements.txt b/functest_requirements.txt
index 774edb421..5fb29530a 100644
--- a/functest_requirements.txt
+++ b/functest_requirements.txt
@@ -1,6 +1,5 @@
 pytest<10
-python-gnupg
 pytest-xdist
 pytest-timeout
 pytest-custom_exit_code
-trustme~=1.2.1
\ No newline at end of file
+trustme~=1.2.1
diff --git a/pulp_container/tests/functional/api/test_push_signatures.py b/pulp_container/tests/functional/api/test_push_signatures.py
index 2d9e3e7f9..dd19652ba 100644
--- a/pulp_container/tests/functional/api/test_push_signatures.py
+++ b/pulp_container/tests/functional/api/test_push_signatures.py
@@ -1,55 +1,78 @@
 """Tests that verify that an image signature can be pushed to Pulp."""
 
 import base64
-import json
+import subprocess
 
 import pytest
 
 from pulp_container.constants import SIGNATURE_TYPE
+from pulp_container.tests.functional.conftest import verify_inline_signature
 from pulp_container.tests.functional.constants import REGISTRY_V2_REPO_PULP
 
 
+def _podman_supports_sq_signing():
+    """Return True if the local podman build supports --sign-by-sq-fingerprint."""
+    result = subprocess.run(
+        ("podman", "push", "--help"),
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+    )
+    return "--sign-by-sq-fingerprint" in result.stdout.decode()
+
+
 @pytest.fixture
-def distribution(
+def signed_distribution(
+    signing_key_home,
     registry_client,
     local_registry,
     container_distribution_api,
-    signing_gpg_metadata,
+    container_namespace_api,
     add_to_cleanup,
     full_path,
 ):
-    """Return a distribution created after pushing a signed content to the Pulp Registry."""
+    """Push an image signed with a Sequoia key (twice, for two distinct signatures).
+
+    Parameterized (via `signing_key_home`) over a key that signs with its primary key and
+    one that signs with a dedicated subkey.
+    """
     if registry_client.name != "podman":
         pytest.skip("This test requires podman to sign pulled content", allow_module_level=True)
+    if not _podman_supports_sq_signing():
+        pytest.skip("This podman build does not support --sign-by-sq-fingerprint")
 
     image_path = f"{REGISTRY_V2_REPO_PULP}:manifest_a"
     registry_client.pull(image_path)
 
-    gpg, fingerprint, keyid = signing_gpg_metadata
-
-    with registry_client.set_env(GNUPGHOME=str(gpg.gnupghome)):
-        local_registry.tag_and_push(image_path, full_path("test-1:manifest_a"), "--sign-by", keyid)
-
-        # push the same image for the second time with a different signature (timestamp)
-        local_registry.tag_and_push(image_path, full_path("test-1:manifest_a"), "--sign-by", keyid)
+    # Point the Sequoia integration at the home holding our imported key.
+    sign_args = ("--sign-by-sq-fingerprint", signing_key_home.fingerprint)
+    with registry_client.set_env(SEQUOIA_HOME=str(signing_key_home.home)):
+        local_registry.tag_and_push(image_path, full_path("test-1:manifest_a"), *sign_args)
+        # push a second time to produce a distinct signature (timestamp)
+        local_registry.tag_and_push(image_path, full_path("test-1:manifest_a"), *sign_args)
 
     distribution = container_distribution_api.list(name="test-1").results[0]
-    add_to_cleanup(container_distribution_api, distribution.pulp_href)
+    # Clean up the namespace, which cascades to the distribution and the push repository.
+    add_to_cleanup(container_namespace_api, distribution.namespace)
 
     return distribution
 
 
 def test_assert_signed_image(
+    signing_key_home,
     local_registry,
     container_repository_api,
     container_manifest_api,
     container_signature_api,
-    signing_gpg_metadata,
-    distribution,
+    signed_distribution,
     full_path,
 ):
-    """Test whether an admin user can fetch a signature from the Pulp Registry."""
-    gpg, fingerprint, keyid = signing_gpg_metadata
+    """Test whether an admin user can fetch a signature from the Pulp Registry.
+
+    Runs against both primary-key and subkey signing.
+    """
+    distribution = signed_distribution
+    fingerprint = signing_key_home.signing_fingerprint
+    keyid = signing_key_home.signing_keyid
 
     repository = container_repository_api.read(distribution.repository)
     manifest = container_manifest_api.list(
@@ -75,13 +98,12 @@ def test_assert_signed_image(
     timestamps = []
     for s in signatures:
         raw_s = base64.b64decode(s["content"])
-        decrypted = gpg.decrypt(raw_s)
-
-        assert decrypted.key_id == keyid
-        assert decrypted.fingerprint == fingerprint
-        assert decrypted.status == "signature valid"
+        sig_fingerprint, sig_key_id, json_s = verify_inline_signature(
+            signing_key_home.public_key, raw_s
+        )
 
-        json_s = json.loads(decrypted.data)
+        assert sig_key_id == keyid
+        assert sig_fingerprint == fingerprint
 
         image_path = json_s["critical"]["identity"]["docker-reference"]
         assert image_path == f"{local_registry.name}/{full_path(distribution)}:manifest_a"
diff --git a/pulp_container/tests/functional/api/test_sign_manifests.py b/pulp_container/tests/functional/api/test_sign_manifests.py
index e0bdaea60..a30b453de 100644
--- a/pulp_container/tests/functional/api/test_sign_manifests.py
+++ b/pulp_container/tests/functional/api/test_sign_manifests.py
@@ -1,14 +1,48 @@
 import pytest
 
+from pulpcore.pytest_plugin import create_signing_service, remove_signing_service
+
 from pulp_container.constants import SIGNATURE_TYPE
 from pulp_container.tests.functional.constants import REGISTRY_V2_REPO_PULP
 
 MANIFEST_TAG = "manifest_a"
 
+# Builds an atomic container signature payload for the passed manifest and signs
+# it with a Sequoia (sq) key, emitting an inline-signed binary OpenPGP message.
+# See https://github.com/pulp/pulp_container/issues/2280.
+SIGNING_SCRIPT_STRING = """#!/usr/bin/env bash
+
+set -e
+
+MANIFEST_PATH=$1
+FINGERPRINT="$PULP_SIGNING_KEY_FINGERPRINT"
+SQ_HOME="{sq_home}"
+
+DIGEST="sha256:$(sha256sum "$MANIFEST_PATH" | awk '{{print $1}}')"
+
+PAYLOAD_FILE="$(mktemp)"
+cat > "$PAYLOAD_FILE" <<EOF
+{{"critical": {{"type": "atomic container signature", \
+"image": {{"docker-manifest-digest": "$DIGEST"}}, \
+"identity": {{"docker-reference": "$REFERENCE"}}}}, \
+"optional": {{"creator": "pulp sq test"}}}}
+EOF
+
+sq --home "$SQ_HOME" sign --signer "$FINGERPRINT" --message --binary \
+   --output "$SIG_PATH" "$PAYLOAD_FILE"
+
+echo "{{\\"signature_path\\": \\"$SIG_PATH\\"}}"
+"""
+
 
 @pytest.fixture
 def distribution(
-    registry_client, local_registry, container_distribution_api, full_path, add_to_cleanup
+    registry_client,
+    local_registry,
+    container_distribution_api,
+    container_namespace_api,
+    full_path,
+    add_to_cleanup,
 ):
     """The fixture for a distribution created by pushing an image to the registry."""
     image_path = f"{REGISTRY_V2_REPO_PULP}:{MANIFEST_TAG}"
@@ -16,35 +50,69 @@ def distribution(
     local_registry.tag_and_push(image_path, full_path(f"test-1:{MANIFEST_TAG}"))
 
     distribution = container_distribution_api.list(name="test-1").results[0]
-    add_to_cleanup(container_distribution_api, distribution.pulp_href)
+    # Clean up the namespace, which cascades to the distribution and the push repository.
+    add_to_cleanup(container_namespace_api, distribution.namespace)
 
     return distribution
 
 
+@pytest.fixture
+def manifest_signing_service(signing_key_home, tmp_path, pulpcore_bindings):
+    """Register a ManifestSigningService backed by a Sequoia key.
+
+    Parameterized (via `signing_key_home`) over a key that signs with its primary key and
+    one that signs with a dedicated subkey.
+    """
+    script_path = tmp_path / "sign-manifest.sh"
+    script_path.write_text(SIGNING_SCRIPT_STRING.format(sq_home=signing_key_home.home))
+    script_path.chmod(0o755)
+
+    try:
+        service_name = create_signing_service(
+            signing_key_home.home,
+            signing_key_home.fingerprint,
+            script_path,
+            backend="sq",
+            service_class="container:ManifestSigningService",
+        )
+    except TypeError:
+        pytest.skip("This pulpcore release does not support the Sequoia (sq) signing backend")
+
+    service = pulpcore_bindings.SigningServicesApi.list(name=service_name).results[0]
+    assert service.pubkey_fingerprint == signing_key_home.fingerprint
+
+    yield service, signing_key_home.signing_fingerprint, signing_key_home.signing_keyid
+
+    remove_signing_service(service_name, service_class="container:ManifestSigningService")
+
+
 def test_sign_manifest(
-    signing_gpg_metadata,
+    manifest_signing_service,
     distribution,
-    container_signing_service,
     container_repository_api,
     container_signature_api,
     container_tag_api,
     container_manifest_api,
     monitor_task,
 ):
-    """Test whether a user can sign a manifest by leveraging a signing service."""
-    _, fingerprint, keyid = signing_gpg_metadata
-    sign_data = {"manifest_signing_service": container_signing_service.pulp_href}
+    """Test whether a user can sign a manifest by leveraging a signing service.
+
+    Runs against both primary-key and subkey signing.
+    """
+    service, fingerprint, keyid = manifest_signing_service
+    sign_data = {"manifest_signing_service": service.pulp_href}
 
     response = container_repository_api.sign(distribution.repository, sign_data)
     created_resources = monitor_task(response.task).created_resources
 
-    tags = container_tag_api.list(repository_version=created_resources[0])
+    repository_version = created_resources[0]
+    tags = container_tag_api.list(repository_version=repository_version)
     assert tags.count == 1
 
     tag = tags.results[0]
     assert tag.name == MANIFEST_TAG
 
-    signatures = container_signature_api.list()
+    signatures = container_signature_api.list(repository_version=repository_version)
     assert signatures.count == 1
 
     signature = signatures.results[0]
diff --git a/pulp_container/tests/functional/conftest.py b/pulp_container/tests/functional/conftest.py
index 990315f94..e51855ff4 100644
--- a/pulp_container/tests/functional/conftest.py
+++ b/pulp_container/tests/functional/conftest.py
@@ -3,12 +3,18 @@
 import stat
 import subprocess
 from contextlib import contextmanager, suppress
+from types import SimpleNamespace
 from urllib.parse import urljoin, urlparse
 from uuid import uuid4
 
 import pytest
 import requests
 
+from pulpcore.pytest_plugin import (
+    KEY_V6_MLDSA65_ED25519_PRIVATE,
+    KEY_V6_MLDSA65_ED25519_PUBLIC,
+    import_signing_key,
+)
 from pulpcore.tests.functional.utils import BindingsNamespace
 
 from pulp_container.tests.functional.constants import PULP_HELLO_WORLD_REPO, REGISTRY_V2_FEED_URL
@@ -17,6 +23,103 @@
     BearerTokenAuth,
 )
 
+# A GPG-generated fixture key. Unlike the Sequoia-generated ML-DSA key (which signs with a
+# dedicated subkey), this key signs with its primary key. Whether a certificate signs with its
+# primary key or a subkey is a matter of key configuration, not tooling -- pulp_container must
+# record the actual signing (sub)key in both cases, which the parameterization below verifies.
+_GPG_FIXTURE_KEY_PRIVATE = (
+    "https://raw.githubusercontent.com/pulp/pulp-fixtures/master/common/"
+    "GPG-PRIVATE-KEY-fixture-signing"
+)
+_GPG_FIXTURE_KEY_PUBLIC = (
+    "https://raw.githubusercontent.com/pulp/pulp-fixtures/master/common/GPG-KEY-fixture-signing"
+)
+
+
+@pytest.fixture(scope="session", params=["primary", "subkey"])
+def signing_key_home(request, tmp_path_factory):
+    """Import a signing key into a Sequoia home, exercising primary- and subkey-signing.
+
+    Yields a namespace with the Sequoia `home`, the certificate `fingerprint` (primary), the
+    actual `signing_fingerprint`/`signing_keyid` used when signing, and the ascii-armored
+    `public_key`.
+    """
+    keys = {
+        # GPG-generated key -> signs with its primary key.
+        "primary": (_GPG_FIXTURE_KEY_PRIVATE, _GPG_FIXTURE_KEY_PUBLIC),
+        # Sequoia ML-DSA (post-quantum) key -> signs with a dedicated subkey.
+        "subkey": (KEY_V6_MLDSA65_ED25519_PRIVATE, KEY_V6_MLDSA65_ED25519_PUBLIC),
+    }
+    private_url, public_url = keys[request.param]
+
+    home = tmp_path_factory.mktemp(f"sq_home_{request.param}")
+    try:
+        _sq, fingerprint, _keyid = import_signing_key(private_url, home, backend="sq")
+    except TypeError:
+        pytest.skip("This pulpcore release does not support the Sequoia (sq) signing backend")
+
+    public_key = requests.get(public_url).content.decode("utf-8")
+    signing_fingerprint, signing_keyid = sq_signing_identity(home, fingerprint, public_key)
+
+    return SimpleNamespace(
+        home=home,
+        fingerprint=fingerprint,
+        signing_fingerprint=signing_fingerprint,
+        signing_keyid=signing_keyid,
+        public_key=public_key,
+    )
+
+
+def _keyid_from_fingerprint(fingerprint):
+    """Derive the key ID from an OpenPGP fingerprint, matching pulp_container's logic.
+
+    For v4 fingerprints (40 hex chars) the key ID is the last 16 chars; for v6 (64 hex
+    chars) it is the first 16 chars.
+    """
+    if len(fingerprint) == 40:
+        return fingerprint[-16:]
+    elif len(fingerprint) == 64:
+        return fingerprint[:16]
+    raise ValueError(f"Unexpected fingerprint length: {len(fingerprint)}")
+
+
+def _verified_signing_key(public_key, raw_signature):
+    """Verify an inline-signed OpenPGP message and return (signing_key_fpr, payload_bytes).
+
+    Works for both classic (RSA/ed25519) and post-quantum (ML-DSA) keys. Uses pysequoia
+    directly rather than pulpcore's gpg_verify because the latter pulls in Django models,
+    which aren't configured in the functional-test client process.
+    """
+    from pysequoia import Cert, verify
+
+    certs = Cert.split_bytes(public_key.encode("utf-8"))
+    result = verify(bytes=raw_signature, store=lambda key_ids: certs)
+    valid_sig = result.valid_sigs[0]
+    return valid_sig.signing_key.upper(), bytes(result.bytes)
+
+
+def verify_inline_signature(public_key, raw_signature):
+    """Verify a signature blob and return (fingerprint, key_id, payload_dict)."""
+    fingerprint, payload_bytes = _verified_signing_key(public_key, raw_signature)
+    return fingerprint, _keyid_from_fingerprint(fingerprint), json.loads(payload_bytes)
+
+
+def sq_signing_identity(sq_home, signer, public_key):
+    """Return the (fingerprint, key_id) actually used when signing with `signer`.
+
+    A certificate may sign with a dedicated subkey rather than its primary key, so the
+    fingerprint recorded on produced signatures can differ from the certificate's primary
+    fingerprint. This signs throwaway data to discover the real signing (sub)key.
+    """
+    completed = subprocess.run(
+        ("sq", "--home", str(sq_home), "sign", "--signer", signer, "--message", "--binary"),
+        input=b"probe",
+        capture_output=True,
+    )
+    completed.check_returncode()
+    fingerprint, _payload = _verified_signing_key(public_key, completed.stdout)
+    return fingerprint, _keyid_from_fingerprint(fingerprint)
+
 
 def gen_container_remote(url=REGISTRY_V2_FEED_URL, **kwargs):
     """Return a semi-random dict for use in creating a container Remote.
diff --git a/pyproject.toml b/pyproject.toml
index b0e385387..89ffacec0 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -26,7 +26,7 @@ dependencies = [
   "jsonschema>=4.4,<4.27",
   "pulpcore>=3.111.0,<3.130",
   "pyjwt[crypto]>=2.4,<2.14",
-  "pysequoia>=0.1.33,<0.2.0"
+  "pysequoia>=0.1.35,<0.2.0"
 ]
 
 [project.urls]