diff --git a/docs/source/user-guide/latest/compatibility.md b/docs/source/user-guide/latest/compatibility.md
index a6cced4e12..adb1e22a2f 100644
--- a/docs/source/user-guide/latest/compatibility.md
+++ b/docs/source/user-guide/latest/compatibility.md
@@ -89,8 +89,6 @@ the [Comet Supported Expressions Guide](expressions.md) for more information on
 
 - **Corr**: Returns null instead of NaN in some edge cases.
   [#2646](https://github.com/apache/datafusion-comet/issues/2646)
-- **First, Last**: These functions are not deterministic. When `ignoreNulls` is set, results may not match Spark.
-  [#1630](https://github.com/apache/datafusion-comet/issues/1630)
 
 ### Struct Expressions
 
diff --git a/spark/src/test/resources/sql-tests/expressions/aggregate/first_last.sql b/spark/src/test/resources/sql-tests/expressions/aggregate/first_last.sql
index 7bc617bffd..8aedc4f5f1 100644
--- a/spark/src/test/resources/sql-tests/expressions/aggregate/first_last.sql
+++ b/spark/src/test/resources/sql-tests/expressions/aggregate/first_last.sql
@@ -17,17 +17,427 @@
 
 -- ConfigMatrix: parquet.enable.dictionary=false,true
 
+-- ============================================================
+-- Setup: shared tables
+-- ============================================================
+
 statement
 CREATE TABLE test_first_last(i int, grp string) USING parquet
 
 statement
 INSERT INTO test_first_last VALUES (1, 'a'), (2, 'a'), (3, 'a'), (NULL, 'b'), (4, 'b')
 
-query spark_answer_only
+statement
+CREATE TABLE test_ignore_nulls(id int, val int, grp string) USING parquet
+
+statement
+INSERT INTO test_ignore_nulls VALUES
+  (1, NULL, 'a'),
+  (2, 10,   'a'),
+  (3, 20,   'a'),
+  (4, NULL, 'b'),
+  (5, 30,   'b'),
+  (6, NULL, 'b')
+
+statement
+CREATE TABLE test_all_nulls(val int, grp string) USING parquet
+
+statement
+INSERT INTO test_all_nulls VALUES (NULL, 'a'), (NULL, 'a'), (NULL, 'b'), (1, 'b')
+
+statement
+CREATE TABLE test_empty(val int) USING parquet
+
+statement
+CREATE TABLE test_single_row(val int) USING parquet
+
+statement
+INSERT INTO test_single_row VALUES (42)
+
+statement
+CREATE TABLE test_single_null(val int) USING parquet
+
+statement
+INSERT INTO test_single_null VALUES (NULL)
+
+statement
+CREATE TABLE test_types(
+  i_val int,
+  l_val bigint,
+  d_val double,
+  s_val string,
+  b_val boolean,
+  grp string
+) USING parquet
+
+statement
+INSERT INTO test_types VALUES
+  (NULL, NULL,  NULL,  NULL,  NULL,  'a'),
+  (1,    100,   1.5,   'foo', true,  'a'),
+  (2,    200,   2.5,   'bar', false, 'a'),
+  (NULL, NULL,  NULL,  NULL,  NULL,  'b'),
+  (NULL, NULL,  NULL,  NULL,  NULL,  'b')
+
+statement
+CREATE TABLE test_null_positions(id int, val int, grp string) USING parquet
+
+statement
+INSERT INTO test_null_positions VALUES
+  (1, NULL, 'start_null'),
+  (2, 10,   'start_null'),
+  (3, 20,   'start_null'),
+  (4, 10,   'mid_null'),
+  (5, NULL, 'mid_null'),
+  (6, 20,   'mid_null'),
+  (7, 10,   'end_null'),
+  (8, 20,   'end_null'),
+  (9, NULL, 'end_null')
+
+statement
+CREATE TABLE test_expr_nulls(val int, grp string) USING parquet
+
+statement
+INSERT INTO test_expr_nulls VALUES (1, 'a'), (2, 'a'), (3, 'a'), (4, 'b'), (5, 'b'), (6, 'b')
+
+statement
+CREATE TABLE test_decimal(val DECIMAL(10,2), grp string) USING parquet
+
+statement
+INSERT INTO test_decimal VALUES (NULL, 'a'), (1.23, 'a'), (4.56, 'a'), (NULL, 'b'), (NULL, 'b')
+
+statement
+CREATE TABLE test_date(val DATE, grp string) USING parquet
+
+statement
+INSERT INTO test_date VALUES (NULL, 'a'), (DATE '2024-01-01', 'a'), (DATE '2024-12-31', 'a'), (NULL, 'b'), (NULL, 'b')
+
+statement
+CREATE TABLE test_large(val int, grp string) USING parquet
+
+statement
+INSERT INTO test_large
+SELECT
+  CASE WHEN id % 10 = 0 THEN id ELSE NULL END as val,
+  CASE WHEN id < 500 THEN 'a' ELSE 'b' END as grp
+FROM (SELECT explode(sequence(1, 1000)) as id)
+
+-- ############################################################
+-- FIRST
+-- ############################################################
+
+-- ============================================================
+-- first: basic (default behavior includes nulls)
+-- ============================================================
+
+query
+SELECT first(i) FROM test_first_last
+
+query
+SELECT first(i, true) FROM test_first_last
+
+query
+SELECT grp, first(i) FROM test_first_last GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: basic
+-- ============================================================
+
+-- without grouping
+query
+SELECT first(val) IGNORE NULLS FROM test_ignore_nulls
+
+-- with grouping
+query
+SELECT grp, first(val) IGNORE NULLS FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+-- contrast: default behavior (RESPECT NULLS) - null can appear as first
+query
+SELECT grp, first(val) FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: all values null in a group
+-- ============================================================
+
+-- group 'a' has all nulls -> should return null even with IGNORE NULLS
+query
+SELECT grp, first(val) IGNORE NULLS FROM test_all_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: empty table
+-- ============================================================
+
+query
+SELECT first(val) IGNORE NULLS FROM test_empty
+
+-- ============================================================
+-- first IGNORE NULLS: single row
+-- ============================================================
+
+query
+SELECT first(val) IGNORE NULLS FROM test_single_row
+
+query
+SELECT first(val) IGNORE NULLS FROM test_single_null
+
+-- ============================================================
+-- first IGNORE NULLS: multiple data types
+-- ============================================================
+
+query expect_fallback(SortAggregate is not supported)
+SELECT grp,
+  first(i_val) IGNORE NULLS,
+  first(l_val) IGNORE NULLS,
+  first(d_val) IGNORE NULLS,
+  first(s_val) IGNORE NULLS,
+  first(b_val) IGNORE NULLS
+FROM test_types GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: nulls at beginning, middle, end
+-- ============================================================
+
+query
+SELECT grp, first(val) IGNORE NULLS FROM test_null_positions GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: boolean parameter form
+-- ============================================================
+
+-- first(val, true) is equivalent to first(val) IGNORE NULLS
+query
+SELECT grp, first(val, true) FROM test_null_positions GROUP BY grp ORDER BY grp
+
+-- first(val, false) is equivalent to first(val) (default, respect nulls)
+query
+SELECT grp, first(val, false) FROM test_null_positions GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: with expressions producing nulls
+-- ============================================================
+
+-- IF expression produces nulls for even values
+query
+SELECT grp,
+  first(IF(val % 2 = 0, NULL, val)) IGNORE NULLS
+FROM test_expr_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: mixed with other aggregations
+-- ============================================================
+
+query
+SELECT grp,
+  first(val) IGNORE NULLS,
+  first(val),
+  count(val),
+  sum(val)
+FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: with HAVING clause
+-- ============================================================
+
+query
+SELECT grp, first(val) IGNORE NULLS as f
+FROM test_ignore_nulls
+GROUP BY grp
+HAVING first(val) IGNORE NULLS IS NOT NULL
+ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: decimal type
+-- ============================================================
+
+query
+SELECT grp, first(val) IGNORE NULLS FROM test_decimal GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: date type
+-- ============================================================
+
+query
+SELECT grp, first(val) IGNORE NULLS FROM test_date GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- first IGNORE NULLS: large group (multi-batch)
+-- ============================================================
+
+query
+SELECT grp, first(val) IGNORE NULLS FROM test_large GROUP BY grp ORDER BY grp
+
+-- ############################################################
+-- LAST
+-- ############################################################
+
+-- ============================================================
+-- last: basic (default behavior includes nulls)
+-- ============================================================
+
+query
+SELECT last(i) FROM test_first_last
+
+query
+SELECT last(i, true) FROM test_first_last
+
+query
+SELECT grp, last(i) FROM test_first_last GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: basic
+-- ============================================================
+
+-- without grouping
+query
+SELECT last(val) IGNORE NULLS FROM test_ignore_nulls
+
+-- with grouping
+query
+SELECT grp, last(val) IGNORE NULLS FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+-- contrast: default behavior (RESPECT NULLS) - null can appear as last
+query
+SELECT grp, last(val) FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: all values null in a group
+-- ============================================================
+
+-- group 'a' has all nulls -> should return null even with IGNORE NULLS
+query
+SELECT grp, last(val) IGNORE NULLS FROM test_all_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: empty table
+-- ============================================================
+
+query
+SELECT last(val) IGNORE NULLS FROM test_empty
+
+-- ============================================================
+-- last IGNORE NULLS: single row
+-- ============================================================
+
+query
+SELECT last(val) IGNORE NULLS FROM test_single_row
+
+query
+SELECT last(val) IGNORE NULLS FROM test_single_null
+
+-- ============================================================
+-- last IGNORE NULLS: multiple data types
+-- ============================================================
+
+query expect_fallback(SortAggregate is not supported)
+SELECT grp,
+  last(i_val) IGNORE NULLS,
+  last(l_val) IGNORE NULLS,
+  last(d_val) IGNORE NULLS,
+  last(s_val) IGNORE NULLS,
+  last(b_val) IGNORE NULLS
+FROM test_types GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: nulls at beginning, middle, end
+-- ============================================================
+
+query
+SELECT grp, last(val) IGNORE NULLS FROM test_null_positions GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: boolean parameter form
+-- ============================================================
+
+-- last(val, true) is equivalent to last(val) IGNORE NULLS
+query
+SELECT grp, last(val, true) FROM test_null_positions GROUP BY grp ORDER BY grp
+
+-- last(val, false) is equivalent to last(val) (default, respect nulls)
+query
+SELECT grp, last(val, false) FROM test_null_positions GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: with expressions producing nulls
+-- ============================================================
+
+-- IF expression produces nulls for even values
+query
+SELECT grp,
+  last(IF(val % 2 = 0, NULL, val)) IGNORE NULLS
+FROM test_expr_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: mixed with other aggregations
+-- ============================================================
+
+query
+SELECT grp,
+  last(val) IGNORE NULLS,
+  last(val),
+  count(val),
+  sum(val)
+FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: with HAVING clause
+-- ============================================================
+
+query
+SELECT grp, last(val) IGNORE NULLS as l
+FROM test_ignore_nulls
+GROUP BY grp
+HAVING last(val) IGNORE NULLS IS NOT NULL
+ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: decimal type
+-- ============================================================
+
+query
+SELECT grp, last(val) IGNORE NULLS FROM test_decimal GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: date type
+-- ============================================================
+
+query
+SELECT grp, last(val) IGNORE NULLS FROM test_date GROUP BY grp ORDER BY grp
+
+-- ============================================================
+-- last IGNORE NULLS: large group (multi-batch)
+-- ============================================================
+
+query
+SELECT grp, last(val) IGNORE NULLS FROM test_large GROUP BY grp ORDER BY grp
+
+-- ############################################################
+-- FIRST + LAST combined
+-- ############################################################
+
+-- ============================================================
+-- first and last together in same query
+-- ============================================================
+
+query
 SELECT first(i), last(i) FROM test_first_last
 
-query spark_answer_only
+query
 SELECT first(i, true), last(i, true) FROM test_first_last
 
-query spark_answer_only
+query
 SELECT grp, first(i), last(i) FROM test_first_last GROUP BY grp ORDER BY grp
+
+query
+SELECT grp,
+  first(val) IGNORE NULLS,
+  last(val) IGNORE NULLS
+FROM test_ignore_nulls GROUP BY grp ORDER BY grp
+
+query
+SELECT grp,
+  first(val) IGNORE NULLS,
+  last(val) IGNORE NULLS,
+  first(val),
+  last(val),
+  count(val),
+  sum(val)
+FROM test_ignore_nulls GROUP BY grp ORDER BY grp
diff --git a/spark/src/test/scala/org/apache/comet/exec/CometAggregateSuite.scala b/spark/src/test/scala/org/apache/comet/exec/CometAggregateSuite.scala
index be60f4aaee..393cb06469 100644
--- a/spark/src/test/scala/org/apache/comet/exec/CometAggregateSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/exec/CometAggregateSuite.scala
@@ -624,8 +624,7 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     }
   }
 
-  // TODO re-enable once https://github.com/apache/datafusion-comet/issues/1646 is implemented
-  ignore("single group-by column + aggregate column, multiple batches, no null") {
+  test("single group-by column + aggregate column, multiple batches, no null") {
     val numValues = 10000
 
     Seq(1, 100, 10000).foreach { numGroups =>
@@ -640,9 +639,10 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
               dictionaryEnabled) {
               withView("v") {
                 sql("CREATE TEMP VIEW v AS SELECT _1, _2 FROM tbl ORDER BY _1")
-                checkSparkAnswerAndOperator(
+                checkSparkAnswerAndFallbackReason(
                   "SELECT _2, SUM(_1), SUM(DISTINCT _1), MIN(_1), MAX(_1), COUNT(_1)," +
-                    " COUNT(DISTINCT _1), AVG(_1), FIRST(_1), LAST(_1) FROM v GROUP BY _2")
+                    " COUNT(DISTINCT _1), AVG(_1), FIRST(_1), LAST(_1) FROM v GROUP BY _2",
+                  "Unsupported aggregation mode PartialMerge")
               }
             }
           }
@@ -651,8 +651,7 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     }
   }
 
-  // TODO re-enable once https://github.com/apache/datafusion-comet/issues/1646 is implemented
-  ignore("multiple group-by columns + single aggregate column (first/last), with nulls") {
+  test("multiple group-by columns + single aggregate column (first/last), with nulls") {
     val numValues = 10000
 
     Seq(1, 100, numValues).foreach { numGroups =>
@@ -727,8 +726,7 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     }
   }
 
-  // TODO re-enable once https://github.com/apache/datafusion-comet/issues/1646 is implemented
-  ignore("multiple group-by columns + multiple aggregate column (first/last), with nulls") {
+  test("multiple group-by columns + multiple aggregate column (first/last), with nulls") {
     val numValues = 10000
 
     Seq(1, 100, numValues).foreach { numGroups =>
@@ -790,8 +788,7 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     }
   }
 
-  // TODO re-enable once https://github.com/apache/datafusion-comet/issues/1646 is implemented
-  ignore("all types first/last, with nulls") {
+  test("all types first/last, with nulls") {
     val numValues = 2048
 
     Seq(1, 100, numValues).foreach { numGroups =>
@@ -803,7 +800,7 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
             Seq(128, numValues + 100).foreach { batchSize =>
               withSQLConf(
                 CometConf.COMET_BATCH_SIZE.key -> batchSize.toString,
-                CometConf.COMET_EXEC_SHUFFLE_ENABLED.key -> "false") {
+                CometConf.COMET_EXEC_SHUFFLE_ENABLED.key -> "true") {
 
                 // Test all combinations of different aggregation & group-by types
                 (1 to 14).foreach { gCol =>
@@ -1168,8 +1165,7 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
     }
   }
 
-  // TODO re-enable once https://github.com/apache/datafusion-comet/issues/1646 is implemented
-  ignore("first/last") {
+  test("first/last") {
     withSQLConf(
       SQLConf.COALESCE_PARTITIONS_ENABLED.key -> "true",
       CometConf.COMET_EXEC_SHUFFLE_ENABLED.key -> "true",
@@ -1185,31 +1181,21 @@ class CometAggregateSuite extends CometTestBase with AdaptiveSparkPlanHelper {
             withView("t") {
               sql("CREATE VIEW t AS SELECT col1, col3 FROM test ORDER BY col1")
 
-              var expectedNumOfCometAggregates = 2
-              checkSparkAnswerAndNumOfAggregates(
-                "SELECT FIRST(col1), LAST(col1) FROM t",
-                expectedNumOfCometAggregates)
+              checkSparkAnswerAndOperator("SELECT FIRST(col1), LAST(col1) FROM t")
 
-              checkSparkAnswerAndNumOfAggregates(
-                "SELECT FIRST(col1), LAST(col1), MIN(col1), COUNT(col1) FROM t",
-                expectedNumOfCometAggregates)
+              checkSparkAnswerAndOperator(
+                "SELECT FIRST(col1), LAST(col1), MIN(col1), COUNT(col1) FROM t")
 
-              checkSparkAnswerAndNumOfAggregates(
-                "SELECT FIRST(col1), LAST(col1), col3 FROM t GROUP BY col3",
-                expectedNumOfCometAggregates)
+              checkSparkAnswerAndOperator(
+                "SELECT FIRST(col1), LAST(col1), col3 FROM t GROUP BY col3")
 
-              checkSparkAnswerAndNumOfAggregates(
-                "SELECT FIRST(col1), LAST(col1), MIN(col1), COUNT(col1), col3 FROM t GROUP BY col3",
-                expectedNumOfCometAggregates)
+              checkSparkAnswerAndOperator(
+                "SELECT FIRST(col1), LAST(col1), MIN(col1), COUNT(col1), col3 FROM t GROUP BY col3")
 
-              expectedNumOfCometAggregates = 0
-              checkSparkAnswerAndNumOfAggregates(
-                "SELECT FIRST(col1, true), LAST(col1) FROM t",
-                expectedNumOfCometAggregates)
+              checkSparkAnswerAndOperator("SELECT FIRST(col1, true), LAST(col1) FROM t")
 
-              checkSparkAnswerAndNumOfAggregates(
-                "SELECT FIRST(col1), LAST(col1, true), col3 FROM t GROUP BY col3",
-                expectedNumOfCometAggregates)
+              checkSparkAnswerAndOperator(
+                "SELECT FIRST(col1), LAST(col1, true), col3 FROM t GROUP BY col3")
             }
           }
         }