diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/RocksDBStateEncoder.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/RocksDBStateEncoder.scala
index c8f68dfd0388f..5acf7cdc9b975 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/RocksDBStateEncoder.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/RocksDBStateEncoder.scala
@@ -624,6 +624,8 @@ class UnsafeRowDataEncoder(
         decodeToUnsafeRow(bytes, reusedKeyRow)
       case PrefixKeyScanStateEncoderSpec(_, numColsPrefixKey) =>
         decodeToUnsafeRow(bytes, numFields = numColsPrefixKey)
+      case _: TimestampAsPrefixKeyStateEncoderSpec | _: TimestampAsPostfixKeyStateEncoderSpec =>
+        decodeToUnsafeRow(bytes, numFields = keySchema.length - 1)
       case _ => throw unsupportedOperationForKeyStateEncoder("decodeKey")
     }
   }
@@ -748,8 +750,15 @@ class AvroStateEncoder(
   )
 
   // Avro schema used by the avro encoders
-  private lazy val keyAvroType: Schema = SchemaConverters.toAvroTypeWithDefaults(keySchema)
-  private lazy val keyProj = UnsafeProjection.create(keySchema)
+  // For timestamp specs, the key part excludes the timestamp column (always the last field).
+  private lazy val effectiveKeySchema: StructType = keyStateEncoderSpec match {
+    case TimestampAsPrefixKeyStateEncoderSpec(s) => StructType(s.dropRight(1))
+    case TimestampAsPostfixKeyStateEncoderSpec(s) => StructType(s.dropRight(1))
+    case _ => keySchema
+  }
+  private lazy val keyAvroType: Schema =
+    SchemaConverters.toAvroTypeWithDefaults(effectiveKeySchema)
+  private lazy val keyProj = UnsafeProjection.create(effectiveKeySchema)
 
   private lazy val valueAvroType: Schema = SchemaConverters.toAvroTypeWithDefaults(valueSchema)
   private lazy val valueProj = UnsafeProjection.create(valueSchema)
@@ -847,8 +856,10 @@ class AvroStateEncoder(
           }
         }
         StructType(remainingSchema)
-      case _ =>
-        throw unsupportedOperationForKeyStateEncoder("createAvroEnc")
+      case TimestampAsPrefixKeyStateEncoderSpec(schema) =>
+        StructType(schema.dropRight(1))
+      case TimestampAsPostfixKeyStateEncoderSpec(schema) =>
+        StructType(schema.dropRight(1))
     }
 
     // Handle suffix key schema for prefix scan case
@@ -1005,6 +1016,11 @@ class AvroStateEncoder(
           StateSchemaIdRow(currentKeySchemaId, avroRow))
       case PrefixKeyScanStateEncoderSpec(_, _) =>
         encodeUnsafeRowToAvro(row, avroEncoder.keySerializer, prefixKeyAvroType, out)
+      case _: TimestampAsPrefixKeyStateEncoderSpec | _: TimestampAsPostfixKeyStateEncoderSpec =>
+        val avroRow =
+          encodeUnsafeRowToAvro(row, avroEncoder.keySerializer, keyAvroType, out)
+        encodeWithStateSchemaId(
+          StateSchemaIdRow(currentKeySchemaId, avroRow))
       case _ => throw unsupportedOperationForKeyStateEncoder("encodeKey")
     }
     prependVersionByte(keyBytes)
@@ -1179,6 +1195,10 @@ class AvroStateEncoder(
       case PrefixKeyScanStateEncoderSpec(_, _) =>
         decodeFromAvroToUnsafeRow(
           bytes, avroEncoder.keyDeserializer, prefixKeyAvroType, prefixKeyProj)
+      case _: TimestampAsPrefixKeyStateEncoderSpec | _: TimestampAsPostfixKeyStateEncoderSpec =>
+        val schemaIdRow = decodeStateSchemaIdRow(bytes)
+        decodeFromAvroToUnsafeRow(
+          schemaIdRow.bytes, avroEncoder.keyDeserializer, keyAvroType, keyProj)
       case _ => throw unsupportedOperationForKeyStateEncoder("decodeKey")
     }
   }
@@ -1782,9 +1802,7 @@ abstract class TimestampKeyStateEncoder(
       rowBytes, Platform.BYTE_ARRAY_OFFSET,
       rowBytesLength
     )
-    // The encoded row does not include the timestamp (it's stored separately),
-    // so decode with keySchema.length - 1 fields.
-    dataEncoder.decodeToUnsafeRow(rowBytes, keySchema.length - 1)
+    dataEncoder.decodeKey(rowBytes)
   }
 
   // NOTE: We reuse the ByteBuffer to avoid allocating a new one for every encoding/decoding,
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStore.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStore.scala
index 8bb1f609b2b44..ec0b8733ec67f 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStore.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStore.scala
@@ -673,7 +673,10 @@ case class RangeKeyScanStateEncoderSpec(
   }
 }
 
-/** The encoder specification for [[TimestampAsPrefixKeyStateEncoder]]. */
+/**
+ * The encoder specification for [[TimestampAsPrefixKeyStateEncoder]].
+ * The encoder expects the provided key schema to have [original key fields..., timestamp field].
+ */
 case class TimestampAsPrefixKeyStateEncoderSpec(keySchema: StructType)
   extends KeyStateEncoderSpec {
 
@@ -688,7 +691,10 @@ case class TimestampAsPrefixKeyStateEncoderSpec(keySchema: StructType)
   }
 }
 
-/** The encoder specification for [[TimestampAsPostfixKeyStateEncoder]]. */
+/**
+ * The encoder specification for [[TimestampAsPostfixKeyStateEncoder]].
+ * The encoder expects the provided key schema to have [original key fields..., timestamp field].
+ */
 case class TimestampAsPostfixKeyStateEncoderSpec(keySchema: StructType)
   extends KeyStateEncoderSpec {
 
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/execution/streaming/state/RocksDBTimestampEncoderOperationsSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/execution/streaming/state/RocksDBTimestampEncoderOperationsSuite.scala
index a65565d8b245e..a9540a4ad623e 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/execution/streaming/state/RocksDBTimestampEncoderOperationsSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/execution/streaming/state/RocksDBTimestampEncoderOperationsSuite.scala
@@ -68,9 +68,7 @@ class RocksDBTimestampEncoderOperationsSuite extends SharedSparkSession
 
   private def newDir(): String = Utils.createTempDir().getCanonicalPath
 
-  // TODO: [SPARK-55145] Address the new state format with Avro and enable the test with Avro
-  //  encoding
-  Seq("unsaferow").foreach { encoding =>
+  Seq("unsaferow", "avro").foreach { encoding =>
     Seq("prefix", "postfix").foreach { encoderType =>
       test(s"Event time as $encoderType: basic put and get operations (encoding = $encoding)") {
         tryWithProviderResource(
@@ -223,9 +221,7 @@ class RocksDBTimestampEncoderOperationsSuite extends SharedSparkSession
     }
   }
 
-  // TODO: [SPARK-55145] Address the new state format with Avro and enable the test with Avro
-  //  encoding
-  Seq("unsaferow").foreach { encoding =>
+  Seq("unsaferow", "avro").foreach { encoding =>
     test(s"Event time as prefix: iterator operations (encoding = $encoding)") {
       tryWithProviderResource(
         newStoreProviderWithTimestampEncoder(
@@ -558,9 +554,7 @@ class RocksDBTimestampEncoderOperationsSuite extends SharedSparkSession
     }
   }
 
-  // TODO: [SPARK-55145] Address the new state format with Avro and enable the test with Avro
-  //  encoding
-  Seq("unsaferow").foreach { encoding =>
+  Seq("unsaferow", "avro").foreach { encoding =>
     Seq("prefix", "postfix").foreach { encoderType =>
       Seq(false, true).foreach { useMultipleValuesPerKey =>
         val multiValueSuffix = if (useMultipleValuesPerKey) " and multiple values" else ""