diff --git a/sdk/python/feast/infra/online_stores/cassandra_online_store/cassandra_online_store.py b/sdk/python/feast/infra/online_stores/cassandra_online_store/cassandra_online_store.py
index 06b0f3ac4d7..631adc11abc 100644
--- a/sdk/python/feast/infra/online_stores/cassandra_online_store/cassandra_online_store.py
+++ b/sdk/python/feast/infra/online_stores/cassandra_online_store/cassandra_online_store.py
@@ -539,17 +539,15 @@ def on_failure(exc, concurrent_queue):
                             feast_value_type = valProto.WhichOneof("val")
                             if feast_value_type == "unix_timestamp_val":
                                 feature_value = (
-                                    valProto.unix_timestamp_val * 1000
-                                )  # Convert to milliseconds
+                                    valProto.unix_timestamp_val
+                                )  # already milliseconds
                             elif feast_value_type is None:
                                 feature_value = None
                             elif feast_value_type in feast_array_types:
                                 if feast_value_type == "unix_timestamp_list_val":
-                                    # Convert list of timestamps to milliseconds
-                                    feature_value = [
-                                        ts * 1000
-                                        for ts in valProto.unix_timestamp_list_val.val  # type:ignore
-                                    ]
+                                    feature_value = list(
+                                        valProto.unix_timestamp_list_val.val  # type:ignore
+                                    )  # already milliseconds
                                 else:
                                     feature_value = getattr(
                                         valProto, str(feast_value_type)
diff --git a/sdk/python/feast/infra/online_stores/eg_valkey.py b/sdk/python/feast/infra/online_stores/eg_valkey.py
index 93f147f51b8..01f5bdf51f4 100644
--- a/sdk/python/feast/infra/online_stores/eg_valkey.py
+++ b/sdk/python/feast/infra/online_stores/eg_valkey.py
@@ -774,9 +774,7 @@ def zset_score(sort_key_value: ValueProto):
         """
         feast_value_type = sort_key_value.WhichOneof("val")
         if feast_value_type == "unix_timestamp_val":
-            feature_value = (
-                sort_key_value.unix_timestamp_val * 1000
-            )  # Convert to milliseconds
+            feature_value = sort_key_value.unix_timestamp_val  # already milliseconds
         else:
             feature_value = getattr(sort_key_value, str(feast_value_type))
         return feature_value
diff --git a/sdk/python/feast/infra/online_stores/redis.py b/sdk/python/feast/infra/online_stores/redis.py
index 8d3d3185ca5..06e90c25586 100644
--- a/sdk/python/feast/infra/online_stores/redis.py
+++ b/sdk/python/feast/infra/online_stores/redis.py
@@ -500,9 +500,7 @@ def zset_score(sort_key_value: ValueProto):
         """
         feast_value_type = sort_key_value.WhichOneof("val")
         if feast_value_type == "unix_timestamp_val":
-            feature_value = (
-                sort_key_value.unix_timestamp_val * 1000
-            )  # Convert to milliseconds
+            feature_value = sort_key_value.unix_timestamp_val  # already milliseconds
         else:
             feature_value = getattr(sort_key_value, str(feast_value_type))
         return feature_value
diff --git a/sdk/python/feast/type_map.py b/sdk/python/feast/type_map.py
index ebf6f0eae19..209bb200d54 100644
--- a/sdk/python/feast/type_map.py
+++ b/sdk/python/feast/type_map.py
@@ -78,11 +78,16 @@ def feast_value_type_to_python_type(field_value_proto: ProtoValue) -> Any:
     if hasattr(val, "val"):
         val = list(val.val)
 
-    # Convert UNIX_TIMESTAMP values to `datetime`
+    # Convert UNIX_TIMESTAMP values to `datetime`.
+    # unix_timestamp_val stores seconds for regular features and milliseconds for sort key
+    # columns. Values > 1e11 are unambiguously ms (current-era seconds ~1.7e9, ms ~1.7e12;
+    # threshold is safe until year ~5138 in seconds).
     if val_attr == "unix_timestamp_list_val":
         val = [
             (
-                datetime.fromtimestamp(v, tz=timezone.utc)
+                datetime.fromtimestamp(
+                    v / 1000.0 if v > 1e11 else float(v), tz=timezone.utc
+                )
                 if v != NULL_TIMESTAMP_INT_VALUE
                 else None
             )
@@ -90,7 +95,9 @@ def feast_value_type_to_python_type(field_value_proto: ProtoValue) -> Any:
         ]
     elif val_attr == "unix_timestamp_val":
         val = (
-            datetime.fromtimestamp(val, tz=timezone.utc)
+            datetime.fromtimestamp(
+                val / 1000.0 if val > 1e11 else float(val), tz=timezone.utc
+            )
             if val != NULL_TIMESTAMP_INT_VALUE
             else None
         )
@@ -358,6 +365,31 @@ def _python_datetime_to_int_timestamp(
     return int_timestamps
 
 
+def _python_datetime_to_int_ms_timestamp(
+    values: Sequence[Any],
+) -> Sequence[Union[int, np.int_]]:
+    """Convert datetime values to milliseconds since epoch (used for sort key columns)."""
+    # Fast path for Numpy array.
+    if isinstance(values, np.ndarray) and isinstance(values.dtype, np.datetime64):
+        if values.ndim != 1:
+            raise ValueError("Only 1 dimensional arrays are supported.")
+        return cast(Sequence[np.int_], values.astype("datetime64[ms]").astype(np.int_))
+
+    int_timestamps = []
+    for value in values:
+        if isinstance(value, datetime):
+            int_timestamps.append(int(round(value.timestamp() * 1000)))
+        elif isinstance(value, Timestamp):
+            int_timestamps.append(int(value.ToMilliseconds()))
+        elif isinstance(value, np.datetime64):
+            int_timestamps.append(value.astype("datetime64[ms]").astype(np.int_))  # type: ignore[attr-defined]
+        elif isinstance(value, type(np.nan)):
+            int_timestamps.append(NULL_TIMESTAMP_INT_VALUE)
+        else:
+            int_timestamps.append(int(value))
+    return int_timestamps
+
+
 def _python_value_to_proto_value(
     feast_value_type: ValueType, values: List[Any]
 ) -> List[ProtoValue]:
diff --git a/sdk/python/feast/utils.py b/sdk/python/feast/utils.py
index af55266c682..2a8ee42625b 100644
--- a/sdk/python/feast/utils.py
+++ b/sdk/python/feast/utils.py
@@ -42,7 +42,10 @@
 from feast.protos.feast.types.Value_pb2 import FloatList as FloatListProto
 from feast.protos.feast.types.Value_pb2 import RepeatedValue as RepeatedValueProto
 from feast.protos.feast.types.Value_pb2 import Value as ValueProto
-from feast.type_map import python_values_to_proto_values
+from feast.type_map import (
+    _python_datetime_to_int_ms_timestamp,
+    python_values_to_proto_values,
+)
 from feast.types import ComplexFeastType, PrimitiveFeastType, from_feast_to_pyarrow_type
 from feast.value_type import ValueType
 from feast.version import get_version
@@ -281,13 +284,27 @@ def _convert_arrow_fv_to_proto(
         (field.name, field.dtype.to_value_type()) for field in feature_view.features
     ] + list(join_keys.items())
 
-    proto_values_by_column = {
-        column: python_values_to_proto_values(
-            table.column(column).to_numpy(zero_copy_only=False), value_type
-        )
-        for column, value_type in columns
+    # Sort key UNIX_TIMESTAMP columns use ms precision so that timestamps differing
+    # by < 1 second produce distinct sort key scores in the online store.
+    sort_key_ts_names = {
+        sk.name
+        for sk in getattr(feature_view, "sort_keys", [])
+        if sk.value_type == ValueType.UNIX_TIMESTAMP
     }
 
+    proto_values_by_column = {}
+    for column, value_type in columns:
+        raw = table.column(column).to_numpy(zero_copy_only=False)
+        if column in sort_key_ts_names:
+            ms_vals = _python_datetime_to_int_ms_timestamp(raw)
+            proto_values_by_column[column] = [
+                ValueProto(unix_timestamp_val=int(ts)) for ts in ms_vals
+            ]
+        else:
+            proto_values_by_column[column] = python_values_to_proto_values(
+                raw, value_type
+            )
+
     entity_keys = [
         EntityKeyProto(
             join_keys=join_keys,
diff --git a/sdk/python/tests/unit/infra/online_store/test_redis.py b/sdk/python/tests/unit/infra/online_store/test_redis.py
index e2aad12bd7e..372cf97923c 100644
--- a/sdk/python/tests/unit/infra/online_store/test_redis.py
+++ b/sdk/python/tests/unit/infra/online_store/test_redis.py
@@ -508,7 +508,9 @@ def _make_rows(n=10):
             {
                 "trip_id": ValueProto(int32_val=i),
                 "rating": ValueProto(float_val=i + 0.5),
-                "event_timestamp": ValueProto(unix_timestamp_val=base_ts + i * 60),
+                "event_timestamp": ValueProto(
+                    unix_timestamp_val=(base_ts + i * 60) * 1000
+                ),
             },
             datetime.fromtimestamp(base_ts + i * 60, tz=timezone.utc),
             None,
diff --git a/sdk/python/tests/unit/infra/online_store/test_valkey.py b/sdk/python/tests/unit/infra/online_store/test_valkey.py
index ed911bcb92a..2af1e8060a1 100644
--- a/sdk/python/tests/unit/infra/online_store/test_valkey.py
+++ b/sdk/python/tests/unit/infra/online_store/test_valkey.py
@@ -402,7 +402,9 @@ def _make_rows(n=10):
             {
                 "trip_id": ValueProto(int32_val=i),
                 "rating": ValueProto(float_val=i + 0.5),
-                "event_timestamp": ValueProto(unix_timestamp_val=base_ts + i * 60),
+                "event_timestamp": ValueProto(
+                    unix_timestamp_val=(base_ts + i * 60) * 1000
+                ),
             },
             datetime.fromtimestamp(base_ts + i * 60, tz=timezone.utc),
             None,