diff --git a/lib/temporal/configuration.rb b/lib/temporal/configuration.rb
index 99e582a2..b93c9dbb 100644
--- a/lib/temporal/configuration.rb
+++ b/lib/temporal/configuration.rb
@@ -3,6 +3,7 @@
 require 'temporal/connection/converter/payload/nil'
 require 'temporal/connection/converter/payload/bytes'
 require 'temporal/connection/converter/payload/json'
+require 'temporal/connection/converter/payload/proto_json'
 require 'temporal/connection/converter/composite'
 
 module Temporal
@@ -39,6 +40,7 @@ class Configuration
       payload_converters: [
         Temporal::Connection::Converter::Payload::Nil.new,
         Temporal::Connection::Converter::Payload::Bytes.new,
+        Temporal::Connection::Converter::Payload::ProtoJSON.new,
         Temporal::Connection::Converter::Payload::JSON.new,
       ]
     ).freeze
diff --git a/lib/temporal/connection/converter/payload/proto_json.rb b/lib/temporal/connection/converter/payload/proto_json.rb
new file mode 100644
index 00000000..994c1e24
--- /dev/null
+++ b/lib/temporal/connection/converter/payload/proto_json.rb
@@ -0,0 +1,35 @@
+require 'temporal/json'
+
+module Temporal
+  module Connection
+    module Converter
+      module Payload
+        class ProtoJSON
+          ENCODING = 'json/protobuf'.freeze
+
+          def encoding
+            ENCODING
+          end
+
+          def from_payload(payload)
+            # TODO: Add error handling.
+            message_type = payload.metadata['messageType']
+            descriptor = Google::Protobuf::DescriptorPool.generated_pool.lookup(message_type)
+            descriptor.msgclass.decode_json(payload.data)
+          end
+
+          def to_payload(data)
+            return unless data.is_a?(Google::Protobuf::MessageExts)
+            Temporal::Api::Common::V1::Payload.new(
+              metadata: {
+                'encoding' => ENCODING,
+                'messageType' => data.class.descriptor.name,
+              },
+              data: data.to_json,
+            )
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/unit/lib/temporal/connection/converter/payload/proto_json_spec.rb b/spec/unit/lib/temporal/connection/converter/payload/proto_json_spec.rb
new file mode 100644
index 00000000..5570d9df
--- /dev/null
+++ b/spec/unit/lib/temporal/connection/converter/payload/proto_json_spec.rb
@@ -0,0 +1,25 @@
+require 'temporal/connection/converter/payload/proto_json'
+
+describe Temporal::Connection::Converter::Payload::ProtoJSON do
+  subject { described_class.new }
+
+  describe 'round trip' do
+    it 'converts' do
+      # Temporal::Api::Common::V1::Payload is a protobuf.
+      # Using it as the "input" here to show the roundtrip.
+      # #to_payload will return a wrapped Payload around this one.
+      input = Temporal::Api::Common::V1::Payload.new(
+        metadata: { 'hello' => 'world' },
+        data: 'hello world',
+      )
+
+      expect(subject.from_payload(subject.to_payload(input))).to eq(input)
+    end
+  end
+
+  it 'skips if not proto message' do
+    input = { hello: 'world' }
+
+    expect(subject.to_payload(input)).to be nil
+  end
+end