diff --git a/proto/message.py b/proto/message.py
index 8ed2a69a..68e5bb0a 100644
--- a/proto/message.py
+++ b/proto/message.py
@@ -332,7 +332,8 @@ def to_json(
         instance,
         *,
         use_integers_for_enums=True,
-        including_default_value_fields=True
+        including_default_value_fields=True,
+        preserving_proto_field_name=False,
     ) -> str:
         """Given a message instance, serialize it to json
 
@@ -342,6 +343,9 @@ def to_json(
             use_integers_for_enums (Optional(bool)): An option that determines whether enum
                 values should be represented by strings (False) or integers (True).
                 Default is True.
+            preserving_proto_field_name (Optional(bool)): An option that
+                determines whether field name representations preserve
+                proto case (snake_case) or use lowerCamelCase. Default is False.
 
         Returns:
             str: The json string representation of the protocol buffer.
@@ -350,6 +354,7 @@ def to_json(
             cls.pb(instance),
             use_integers_for_enums=use_integers_for_enums,
             including_default_value_fields=including_default_value_fields,
+            preserving_proto_field_name=preserving_proto_field_name,
         )
 
     def from_json(cls, payload, *, ignore_unknown_fields=False) -> "Message":
@@ -620,7 +625,7 @@ def __init__(
         package: str,
         full_name: str,
         marshal: Marshal,
-        options: descriptor_pb2.MessageOptions
+        options: descriptor_pb2.MessageOptions,
     ) -> None:
         self.package = package
         self.full_name = full_name
diff --git a/tests/test_json.py b/tests/test_json.py
index 4b7be8be..d1cbc1fb 100644
--- a/tests/test_json.py
+++ b/tests/test_json.py
@@ -136,3 +136,15 @@ class Octopus(proto.Message):
     # Don't permit unknown fields by default
     with pytest.raises(ParseError):
         o = Octopus.from_json(json_str)
+
+
+def test_json_snake_case():
+    class Squid(proto.Message):
+        mass_kg = proto.Field(proto.INT32, number=1)
+
+    json_str = '{\n  "mass_kg": 20\n}'
+    s = Squid.from_json(json_str)
+
+    assert s.mass_kg == 20
+
+    assert Squid.to_json(s, preserving_proto_field_name=True) == json_str