Montgomery signed for Rotherham United in the summer of 2003 as a young understudy for Mike Pollitt. Montgomery made his debut for Rotherham as a late substitute against Crystal Palace, coming on after Pollitt had been sent off for handball outside of his area.
In the summer of 2003, Montgomery joined Rotherham United as an understudy to Mike Pollitt. He made his first appearance for the club as a substitute in a match against Crystal Palace, replacing Pollitt after he was sent off for handling the ball outside his penalty area.