diff --git a/common/src/main/java/dev/cel/common/internal/BUILD.bazel b/common/src/main/java/dev/cel/common/internal/BUILD.bazel
index e373f442b..b76338cef 100644
--- a/common/src/main/java/dev/cel/common/internal/BUILD.bazel
+++ b/common/src/main/java/dev/cel/common/internal/BUILD.bazel
@@ -128,6 +128,7 @@ java_library(
         "@maven//:com_google_errorprone_error_prone_annotations",
         "@maven//:com_google_guava_guava",
         "@maven//:com_google_protobuf_protobuf_java",
+        "@maven//:com_google_protobuf_protobuf_java_util",
         "@maven//:org_jspecify_jspecify",
     ],
 )
diff --git a/common/src/main/java/dev/cel/common/internal/ProtoAdapter.java b/common/src/main/java/dev/cel/common/internal/ProtoAdapter.java
index 6e291c626..194e8260d 100644
--- a/common/src/main/java/dev/cel/common/internal/ProtoAdapter.java
+++ b/common/src/main/java/dev/cel/common/internal/ProtoAdapter.java
@@ -50,6 +50,8 @@
 import com.google.protobuf.UInt32Value;
 import com.google.protobuf.UInt64Value;
 import com.google.protobuf.Value;
+import com.google.protobuf.util.Durations;
+import com.google.protobuf.util.Timestamps;
 import dev.cel.common.CelErrorCode;
 import dev.cel.common.CelRuntimeException;
 import dev.cel.common.annotations.Internal;
@@ -475,6 +477,15 @@ public Optional<Message> adaptValueToProto(Object value, String protoTypeName) {
         return json.setListValue(listValue).build();
       }
     }
+    if (value instanceof Timestamp) {
+      // CEL follows the proto3 to JSON conversion which formats as an RFC 3339 encoded JSON string.
+      String ts = Timestamps.toString((Timestamp) value);
+      return json.setStringValue(ts).build();
+    }
+    if (value instanceof Duration) {
+      String duration = Durations.toString((Duration) value);
+      return json.setStringValue(duration).build();
+    }
     return null;
   }
 
diff --git a/runtime/src/test/resources/jsonConversions.baseline b/runtime/src/test/resources/jsonConversions.baseline
new file mode 100644
index 000000000..3c674b1c4
--- /dev/null
+++ b/runtime/src/test/resources/jsonConversions.baseline
@@ -0,0 +1,12 @@
+Source: google.protobuf.Struct { fields: {'timestamp': ts, 'duration': du } }
+declare ts {
+  value google.protobuf.Timestamp
+}
+declare du {
+  value google.protobuf.Duration
+}
+=====>
+bindings: {ts=seconds: 100
+, du=nanos: 200000000
+}
+result:   {timestamp=1970-01-01T00:01:40Z, duration=0.200s}
diff --git a/testing/src/main/java/dev/cel/testing/BaseInterpreterTest.java b/testing/src/main/java/dev/cel/testing/BaseInterpreterTest.java
index 0addafaf9..17e6bc26c 100644
--- a/testing/src/main/java/dev/cel/testing/BaseInterpreterTest.java
+++ b/testing/src/main/java/dev/cel/testing/BaseInterpreterTest.java
@@ -1725,6 +1725,16 @@ public void jsonValueTypes() throws Exception {
     runTest(Activation.of("x", xStruct));
   }
 
+  @Test
+  public void jsonConversions() throws Exception {
+    declareVariable("ts", CelTypes.TIMESTAMP);
+    declareVariable("du", CelTypes.DURATION);
+    source = "google.protobuf.Struct { fields: {'timestamp': ts, 'duration': du } }";
+    runTest(
+        Activation.copyOf(
+            ImmutableMap.of("ts", Timestamps.fromSeconds(100), "du", Durations.fromMillis(200))));
+  }
+
   @Test
   public void typeComparisons() throws Exception {
     container = TestAllTypes.getDescriptor().getFile().getPackage();