He started his hockey career in the Ontario Provincial Junior A Hockey League. He played 3 games with the Syracuse Jr. Crunch and 1 seasons with the Buffalo Lightning. He also played in the Ontario Hockey League (OHL) with the Guelph Storm for 4 seasons. He was drafted by the New York Rangers with the 127th overall pick in the 2004 NHL Entry Draft. He played one season with the Hartford Wolf Pack of the American Hockey League (AHL) before being called up to the Ranger's main roster. On September 12, 2011, Callahan was named the captain of the Rangers.