Concatenate two column values in LinQ Lambda Expression

You can use string concatenation:

select new
{
    Username = CurrentUser.First_Name + " " + CurrentUser.Last_Name,
    CurrentUser.Email_ID,
    CurrentUser.GUID
};

Try

     select new
            {
                          FullName = CurrentUser.First_Name + " " + CurrentUser.Last_Name,
                          CurrentUser.Email_ID,
                          CurrentUser.GUID
            };

You should give your anonymous type 'keys' (read-only properties):

select new
{
  Name = CurrentUser.First_Name + " " + CurrentUser.Last_Name,
};

And then just concatenate the string on assigning the user name.

var allUserList = from CurrentUser in objDataContext.Users.Where(c => c.Is_Deleted != false)                              
                  select new
                  {
                      Name = CurrentUser.First_Name + " " + CurrentUser.Last_Name, 
                      CurrentUser.Email_ID,
                      CurrentUser.GUID
                  };