Json.NET in Unity throwing 'The type or namespace `Newtonsoft` could not be found'

1.In Unity, place the Newtonsoft.Json.dll file into the Assets/Plugins folder

2.In Visual Studio, highlight Analyzers in the in Solution Explorer window.

3.Go to Project-> Add Reference and choose your project directory followed by Assets/Plugin. That's it.

Optional:

In Unity 5.3, Unity added native support of Json serialization. You can simply use that to convert to Json and back to class.