diff --git a/docs/spark_expressions_support.md b/docs/spark_expressions_support.md
index 5474894108..8b4d80a2bf 100644
--- a/docs/spark_expressions_support.md
+++ b/docs/spark_expressions_support.md
@@ -400,7 +400,7 @@
 ### string_funcs
 
 - [x] ascii
-- [ ] base64
+- [x] base64
 - [x] bit_length
 - [x] btrim
 - [x] char
diff --git a/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala b/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
index 9d13ccd9ed..b7514c05b0 100644
--- a/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/QueryPlanSerde.scala
@@ -148,6 +148,7 @@ object QueryPlanSerde extends Logging with CometExprShim {
 
   private val stringExpressions: Map[Class[_ <: Expression], CometExpressionSerde[_]] = Map(
     classOf[Ascii] -> CometScalarFunction("ascii"),
+    classOf[Base64] -> CometBase64,
     classOf[BitLength] -> CometScalarFunction("bit_length"),
     classOf[Chr] -> CometScalarFunction("char"),
     classOf[ConcatWs] -> CometConcatWs,
diff --git a/spark/src/main/scala/org/apache/comet/serde/statics.scala b/spark/src/main/scala/org/apache/comet/serde/statics.scala
index 0737644ab9..372f209eff 100644
--- a/spark/src/main/scala/org/apache/comet/serde/statics.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/statics.scala
@@ -19,11 +19,13 @@
 
 package org.apache.comet.serde
 
-import org.apache.spark.sql.catalyst.expressions.Attribute
+import org.apache.spark.sql.catalyst.expressions.{Attribute, Base64, Literal}
 import org.apache.spark.sql.catalyst.expressions.objects.StaticInvoke
 import org.apache.spark.sql.catalyst.util.CharVarcharCodegenUtils
+import org.apache.spark.sql.types.BooleanType
 
 import org.apache.comet.CometSparkSessionExtensions.withInfo
+import org.apache.comet.serde.QueryPlanSerde.{exprToProtoInternal, optExprWithInfo, scalarFunctionExprToProto}
 
 object CometStaticInvoke extends CometExpressionSerde[StaticInvoke] {
 
@@ -34,7 +36,8 @@ object CometStaticInvoke extends CometExpressionSerde[StaticInvoke] {
       : Map[(String, Class[_]), CometExpressionSerde[StaticInvoke]] =
     Map(
       ("readSidePadding", classOf[CharVarcharCodegenUtils]) -> CometScalarFunction(
-        "read_side_padding"))
+        "read_side_padding"),
+      ("encode", classOf[Base64]) -> CometBase64Encode)
 
   override def convert(
       expr: StaticInvoke,
@@ -52,3 +55,27 @@ object CometStaticInvoke extends CometExpressionSerde[StaticInvoke] {
     }
   }
 }
+
+/**
+ * Handler for Base64.encode StaticInvoke (Spark 3.5+, where Base64 is RuntimeReplaceable). Maps
+ * to DataFusion's built-in encode(input, 'base64') function.
+ */
+private object CometBase64Encode extends CometExpressionSerde[StaticInvoke] {
+
+  override def convert(
+      expr: StaticInvoke,
+      inputs: Seq[Attribute],
+      binding: Boolean): Option[ExprOuterClass.Expr] = {
+    // Check if chunked mode is requested (2nd argument, Spark 3.5+)
+    expr.arguments match {
+      case Seq(_, Literal(true, BooleanType)) =>
+        withInfo(expr, "base64 with chunk encoding is not supported")
+        return None
+      case _ => // OK: either no chunkBase64 param (Spark 3.4) or chunkBase64=false
+    }
+    val inputExpr = exprToProtoInternal(expr.arguments.head, inputs, binding)
+    val encodingExpr = exprToProtoInternal(Literal("base64"), inputs, binding)
+    val optExpr = scalarFunctionExprToProto("encode", inputExpr, encodingExpr)
+    optExprWithInfo(optExpr, expr, expr.arguments.head)
+  }
+}
diff --git a/spark/src/main/scala/org/apache/comet/serde/strings.scala b/spark/src/main/scala/org/apache/comet/serde/strings.scala
index 64ba644048..a10c65519b 100644
--- a/spark/src/main/scala/org/apache/comet/serde/strings.scala
+++ b/spark/src/main/scala/org/apache/comet/serde/strings.scala
@@ -21,7 +21,7 @@ package org.apache.comet.serde
 
 import java.util.Locale
 
-import org.apache.spark.sql.catalyst.expressions.{Attribute, Cast, Concat, ConcatWs, Expression, If, InitCap, IsNull, Left, Length, Like, Literal, Lower, RegExpReplace, Right, RLike, StringLPad, StringRepeat, StringRPad, StringSplit, Substring, Upper}
+import org.apache.spark.sql.catalyst.expressions.{Attribute, Base64, Cast, Concat, ConcatWs, Expression, If, InitCap, IsNull, Left, Length, Like, Literal, Lower, RegExpReplace, Right, RLike, StringLPad, StringRepeat, StringRPad, StringSplit, Substring, Upper}
 import org.apache.spark.sql.types.{BinaryType, DataTypes, LongType, StringType}
 import org.apache.spark.unsafe.types.UTF8String
 
@@ -31,6 +31,23 @@ import org.apache.comet.expressions.{CometCast, CometEvalMode, RegExp}
 import org.apache.comet.serde.ExprOuterClass.Expr
 import org.apache.comet.serde.QueryPlanSerde.{createBinaryExpr, exprToProtoInternal, optExprWithInfo, scalarFunctionExprToProto, scalarFunctionExprToProtoWithReturnType}
 
+/**
+ * Handler for Base64 as a direct expression (Spark 3.4 where it is not RuntimeReplaceable). In
+ * Spark 3.5+, Base64 is RuntimeReplaceable and handled via CometBase64Encode in statics.scala.
+ */
+object CometBase64 extends CometExpressionSerde[Base64] {
+
+  override def convert(
+      expr: Base64,
+      inputs: Seq[Attribute],
+      binding: Boolean): Option[ExprOuterClass.Expr] = {
+    val inputExpr = exprToProtoInternal(expr.child, inputs, binding)
+    val encodingExpr = exprToProtoInternal(Literal("base64"), inputs, binding)
+    val optExpr = scalarFunctionExprToProto("encode", inputExpr, encodingExpr)
+    optExprWithInfo(optExpr, expr, expr.child)
+  }
+}
+
 object CometStringRepeat extends CometExpressionSerde[StringRepeat] {
 
   override def convert(
diff --git a/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala b/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala
index 121d7f7d5a..c591739527 100644
--- a/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala
@@ -148,6 +148,31 @@ class CometStringExpressionSuite extends CometTestBase {
     }
   }
 
+  test("base64") {
+    withSQLConf("spark.sql.chunkBase64String.enabled" -> "false") {
+      val data = Seq(
+        Array[Byte](72, 101, 108, 108, 111), // "Hello"
+        Array[Byte](83, 112, 97, 114, 107, 32, 83, 81, 76), // "Spark SQL"
+        Array[Byte](), // empty
+        null).map(Tuple1(_))
+      withParquetTable(data, "tbl") {
+        checkSparkAnswerAndOperator("SELECT base64(_1) FROM tbl")
+        checkSparkAnswerAndOperator("SELECT base64(NULL) FROM tbl")
+      }
+    }
+  }
+
+  test("base64 with chunk encoding falls back") {
+    withSQLConf("spark.sql.chunkBase64String.enabled" -> "true") {
+      val data = Seq(Array[Byte](72, 101, 108, 108, 111)).map(Tuple1(_))
+      withParquetTable(data, "tbl") {
+        checkSparkAnswerAndFallbackReason(
+          "SELECT base64(_1) FROM tbl",
+          "base64 with chunk encoding is not supported")
+      }
+    }
+  }
+
   test("split string basic") {
     withSQLConf("spark.comet.expression.StringSplit.allowIncompatible" -> "true") {
       withParquetTable((0 until 5).map(i => (s"value$i,test$i", i)), "tbl") {