The 25-year-old has signed a four-year contract from Rangers after agreeing personal terms and passing a Boro medical.
Gordon Strachan said: Kevin knows the game and he's got great determination about him, very much in the Robbo (Barry Robson) mould.
He's also a more disciplined player than most but he isn't just a sitting midfielder. He's a very good passer, he retains the ball well and he scored some important goals in Scotland. He's an excellent signing.
Source: Northern Echo
Source: Northern Echo