How to return a 200 HTTP Status Code from ASP.NET MVC 3 controller

200 is just the normal HTTP header for a successful request. If that's all you need, just have the controller return new EmptyResult();

In your controller you'd return an HttpStatusCodeResult like this...

[HttpPost]
public ActionResult SomeMethod(...your method parameters go here...)
{
   // todo: put your processing code here

   //If not using MVC5
   return new HttpStatusCodeResult(200);

   //If using MVC5
   return new HttpStatusCodeResult(HttpStatusCode.OK);  // OK = 200
}

You can simply set the status code of the response to 200 like the following

public ActionResult SomeMethod(parameters...)
{
   //others code here
   ...      
   Response.StatusCode = 200;
   return YourObject;  
}