Deserialize json string to object c#.net

Your JSON represents an object with trn as a property within another object. So you need to represent that in your code, as well. For example:

using System;
using System.IO;
using Newtonsoft.Json;

public class Transaction
{
    [JsonProperty("visited_date")]
    public DateTime VisitedDate { get; set; }
    [JsonProperty("party_code")]
    public string PartyCode { get; set; }
    [JsonProperty("response")]
    public string Response { get; set; }
    [JsonProperty("response_type")]    
    public string ResponseType { get; set; }
    [JsonProperty("time_stamp")]
    public DateTime Timestamp { get; set; }
    [JsonProperty("trans_id")]
    public string TransactionId { get; set; }
    [JsonProperty("total_amount")]    
    public double TotalAmount { get; set; }
    [JsonProperty("discount")]
    public double Discount { get; set; }
}

public class TransactionWrapper
{
    [JsonProperty("trn")]
    public Transaction Transaction { get; set; }
}

class Test
{
    static void Main(string[] args)
    {
        string json = "{\"trn\":{\"visited_date\":\"2015-04-05\",\"party_code\":\"8978a1bf-c88b-11e4-a815-00ff2dce0943\",\"response\":\"Reason 5\",\"response_type\":\"NoOrder\",\"time_stamp\":\"2015-04-05 18:27:42\",\"trans_id\":\"8e15f00b288a701e60a08f968a42a560\",\"total_amount\":0.0,\"discount\":0.0}}";
        var wrapper = JsonConvert.DeserializeObject<TransactionWrapper>(json);
        Console.WriteLine(wrapper.Transaction.PartyCode);
    }
}

Note how I've used the [JsonProperty] attribute to allow the property names themselves to be idiomatic for .NET, but the JSON property names to still be used appropriately. I've also changed the types of Transaction and VisitedDate. Finally, it's slightly alarming that total_amount and discount are double values - that's really not suitable for currency values. Unfortunately, you may not be able to control that.