Odata Controller: How to convert Odata response to C# object at client

The OData response contains a string, not an instance of myValidationResult. Also, the response looks like it's missing some backslashes. (Are you sure the response shown is exactly what you received from the service?)

You can either fix the serialization of myValidationResult on the service:

// Don't serialize vResult yourself. OData will do it for you.
var resp = Content(HttpStatusCode.BadRequest, vResult );

Or deserialize in two steps as follows.

var data = "{\r\n \"@odata.context\":\"http://localhost/ApplicationService/model/$metadata#Edm.String\",\"value\":\"{\\\"Messages\\\":[\\\"message 1\\\",\\\"message 2\\\",\\\"message 3\\\",\\\"message 4\\\"],\\\"IsValidEntity\\\":false}\"\r\n}";
var outer = Newtonsoft.Json.JsonConvert.DeserializeObject<OData<string>>(data);
var inner = Newtonsoft.Json.JsonConvert.DeserializeObject<myValidationResult>(outer.value);

One more thing: The JsonProperty on OData<T> should be named @odata.context.