diff --git a/native/core/src/execution/planner.rs b/native/core/src/execution/planner.rs
index ac35925ace..d907611322 100644
--- a/native/core/src/execution/planner.rs
+++ b/native/core/src/execution/planner.rs
@@ -149,6 +149,25 @@ struct JoinParameters {
     pub join_type: DFJoinType,
 }
 
+/// If `expr` evaluates to `Timestamp(_, Some(_))` against `schema`, wrap it in a
+/// metadata-only cast to `Timestamp(_, None)`. This is required because
+/// DataFusion's `SortMergeJoinExec` comparator only supports timezone-less
+/// timestamp types, while Spark's `TimestampType` serializes as
+/// `Timestamp(µs, "UTC")`. The cast preserves ordering on the same time unit.
+fn strip_timestamp_tz(
+    expr: Arc<dyn PhysicalExpr>,
+    schema: &Schema,
+) -> Result<Arc<dyn PhysicalExpr>, ExecutionError> {
+    match expr.data_type(schema)? {
+        DataType::Timestamp(unit, Some(_)) => Ok(Arc::new(CastExpr::new(
+            expr,
+            DataType::Timestamp(unit, None),
+            None,
+        ))),
+        _ => Ok(expr),
+    }
+}
+
 #[derive(Default)]
 pub struct BinaryExprOptions {
     pub is_integral_div: bool,
@@ -1630,10 +1649,23 @@ impl PhysicalPlanner {
                 let left = Arc::clone(&join_params.left.native_plan);
                 let right = Arc::clone(&join_params.right.native_plan);
 
+                let left_schema = left.schema();
+                let right_schema = right.schema();
+                let join_on = join_params
+                    .join_on
+                    .into_iter()
+                    .map(|(l, r)| {
+                        Ok((
+                            strip_timestamp_tz(l, left_schema.as_ref())?,
+                            strip_timestamp_tz(r, right_schema.as_ref())?,
+                        ))
+                    })
+                    .collect::<Result<Vec<_>, ExecutionError>>()?;
+
                 let join = Arc::new(SortMergeJoinExec::try_new(
                     Arc::clone(&left),
                     Arc::clone(&right),
-                    join_params.join_on,
+                    join_on,
                     join_params.join_filter,
                     join_params.join_type,
                     sort_options,
diff --git a/spark/src/main/scala/org/apache/spark/sql/comet/operators.scala b/spark/src/main/scala/org/apache/spark/sql/comet/operators.scala
index a9c065d726..109aa3f44f 100644
--- a/spark/src/main/scala/org/apache/spark/sql/comet/operators.scala
+++ b/spark/src/main/scala/org/apache/spark/sql/comet/operators.scala
@@ -43,7 +43,7 @@ import org.apache.spark.sql.execution.exchange.ReusedExchangeExec
 import org.apache.spark.sql.execution.joins.{BroadcastHashJoinExec, HashJoin, ShuffledHashJoinExec, SortMergeJoinExec}
 import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}
 import org.apache.spark.sql.internal.SQLConf
-import org.apache.spark.sql.types.{ArrayType, BooleanType, ByteType, DataType, DateType, DecimalType, DoubleType, FloatType, IntegerType, LongType, MapType, ShortType, StringType, TimestampNTZType}
+import org.apache.spark.sql.types.{ArrayType, BooleanType, ByteType, DataType, DateType, DecimalType, DoubleType, FloatType, IntegerType, LongType, MapType, ShortType, StringType, TimestampNTZType, TimestampType}
 import org.apache.spark.sql.vectorized.ColumnarBatch
 import org.apache.spark.util.SerializableConfiguration
 import org.apache.spark.util.io.ChunkedByteBuffer
@@ -2094,7 +2094,7 @@ object CometSortMergeJoinExec extends CometOperatorSerde[SortMergeJoinExec] {
     case _: ByteType | _: ShortType | _: IntegerType | _: LongType | _: FloatType |
         _: DoubleType | _: StringType | _: DateType | _: DecimalType | _: BooleanType =>
       true
-    case TimestampNTZType => true
+    case TimestampNTZType | _: TimestampType => true
     case _ => false
   }
 
diff --git a/spark/src/test/scala/org/apache/comet/exec/CometJoinSuite.scala b/spark/src/test/scala/org/apache/comet/exec/CometJoinSuite.scala
index 49fbe10c30..b30733181e 100644
--- a/spark/src/test/scala/org/apache/comet/exec/CometJoinSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/exec/CometJoinSuite.scala
@@ -25,7 +25,7 @@ import org.scalatest.Tag
 import org.apache.spark.sql.CometTestBase
 import org.apache.spark.sql.catalyst.TableIdentifier
 import org.apache.spark.sql.catalyst.analysis.UnresolvedRelation
-import org.apache.spark.sql.comet.{CometBroadcastExchangeExec, CometBroadcastHashJoinExec}
+import org.apache.spark.sql.comet.{CometBroadcastExchangeExec, CometBroadcastHashJoinExec, CometSortMergeJoinExec}
 import org.apache.spark.sql.internal.SQLConf
 
 import org.apache.comet.CometConf
@@ -54,21 +54,119 @@ class CometJoinSuite extends CometTestBase {
         .toSeq)
   }
 
-  test("SortMergeJoin with unsupported key type should fall back to Spark") {
+  test("SortMergeJoin with TimestampType key runs natively") {
     withSQLConf(
       SQLConf.SESSION_LOCAL_TIMEZONE.key -> "Asia/Kathmandu",
       SQLConf.ADAPTIVE_AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
-      SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1") {
+      SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.PREFER_SORTMERGEJOIN.key -> "true") {
       withTable("t1", "t2") {
         sql("CREATE TABLE t1(name STRING, time TIMESTAMP) USING PARQUET")
-        sql("INSERT OVERWRITE t1 VALUES('a', timestamp'2019-01-01 11:11:11')")
+        sql(
+          "INSERT OVERWRITE t1 VALUES " +
+            "('a', timestamp'2019-01-01 11:11:11'), " +
+            "('b', timestamp'2020-05-05 05:05:05')")
 
         sql("CREATE TABLE t2(name STRING, time TIMESTAMP) USING PARQUET")
-        sql("INSERT OVERWRITE t2 VALUES('a', timestamp'2019-01-01 11:11:11')")
+        sql(
+          "INSERT OVERWRITE t2 VALUES " +
+            "('a', timestamp'2019-01-01 11:11:11'), " +
+            "('c', timestamp'2021-07-07 07:07:07')")
+
+        checkSparkAnswerAndOperator(
+          sql("SELECT * FROM t1 JOIN t2 ON t1.time = t2.time"),
+          Seq(classOf[CometSortMergeJoinExec]))
+      }
+    }
+  }
+
+  test("SortMergeJoin with TimestampType key supports outer joins") {
+    withSQLConf(
+      SQLConf.SESSION_LOCAL_TIMEZONE.key -> "Asia/Kathmandu",
+      SQLConf.ADAPTIVE_AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.PREFER_SORTMERGEJOIN.key -> "true") {
+      withTable("t1", "t2") {
+        sql("CREATE TABLE t1(id INT, time TIMESTAMP) USING PARQUET")
+        sql(
+          "INSERT OVERWRITE t1 VALUES " +
+            "(1, timestamp'2019-01-01 11:11:11'), " +
+            "(2, timestamp'2020-05-05 05:05:05'), " +
+            "(3, timestamp'2021-07-07 07:07:07')")
+
+        sql("CREATE TABLE t2(id INT, time TIMESTAMP) USING PARQUET")
+        sql(
+          "INSERT OVERWRITE t2 VALUES " +
+            "(10, timestamp'2019-01-01 11:11:11'), " +
+            "(20, timestamp'2022-02-02 02:02:02')")
+
+        for (joinType <- Seq("LEFT OUTER", "RIGHT OUTER", "FULL OUTER")) {
+          checkSparkAnswerAndOperator(
+            sql(s"SELECT * FROM t1 $joinType JOIN t2 ON t1.time = t2.time"),
+            Seq(classOf[CometSortMergeJoinExec]))
+        }
+      }
+    }
+  }
 
-        val df = sql("SELECT * FROM t1 JOIN t2 ON t1.time = t2.time")
-        val (sparkPlan, cometPlan) = checkSparkAnswer(df)
-        assert(sparkPlan.canonicalized === cometPlan.canonicalized)
+  test("SortMergeJoin with composite (string, timestamp) key runs natively") {
+    withSQLConf(
+      SQLConf.ADAPTIVE_AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.PREFER_SORTMERGEJOIN.key -> "true") {
+      withTable("t1", "t2") {
+        sql("CREATE TABLE t1(name STRING, time TIMESTAMP) USING PARQUET")
+        sql(
+          "INSERT OVERWRITE t1 VALUES " +
+            "('a', timestamp'2019-01-01 11:11:11'), " +
+            "('b', timestamp'2019-01-01 11:11:11'), " +
+            "('a', timestamp'2020-05-05 05:05:05')")
+
+        sql("CREATE TABLE t2(name STRING, time TIMESTAMP) USING PARQUET")
+        sql(
+          "INSERT OVERWRITE t2 VALUES " +
+            "('a', timestamp'2019-01-01 11:11:11'), " +
+            "('b', timestamp'2020-05-05 05:05:05'), " +
+            "('a', timestamp'2020-05-05 05:05:05')")
+
+        checkSparkAnswerAndOperator(
+          sql(
+            "SELECT * FROM t1 JOIN t2 " +
+              "ON t1.name = t2.name AND t1.time = t2.time"),
+          Seq(classOf[CometSortMergeJoinExec]))
+      }
+    }
+  }
+
+  test("SortMergeJoin with nullable TimestampType key runs natively") {
+    withSQLConf(
+      SQLConf.ADAPTIVE_AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1",
+      SQLConf.PREFER_SORTMERGEJOIN.key -> "true") {
+      withTable("t1", "t2") {
+        sql("CREATE TABLE t1(id INT, time TIMESTAMP) USING PARQUET")
+        sql(
+          "INSERT OVERWRITE t1 VALUES " +
+            "(1, timestamp'2019-01-01 11:11:11'), " +
+            "(2, CAST(NULL AS TIMESTAMP)), " +
+            "(3, timestamp'2020-05-05 05:05:05')")
+
+        sql("CREATE TABLE t2(id INT, time TIMESTAMP) USING PARQUET")
+        sql(
+          "INSERT OVERWRITE t2 VALUES " +
+            "(10, timestamp'2019-01-01 11:11:11'), " +
+            "(20, CAST(NULL AS TIMESTAMP)), " +
+            "(30, timestamp'2022-02-02 02:02:02')")
+
+        // Inner join: NULL = NULL must not match in Spark semantics.
+        checkSparkAnswerAndOperator(
+          sql("SELECT * FROM t1 JOIN t2 ON t1.time = t2.time"),
+          Seq(classOf[CometSortMergeJoinExec]))
+
+        // Full outer join: NULL-keyed rows from both sides surface as unmatched.
+        checkSparkAnswerAndOperator(
+          sql("SELECT * FROM t1 FULL OUTER JOIN t2 ON t1.time = t2.time"),
+          Seq(classOf[CometSortMergeJoinExec]))
       }
     }
   }