Horton played hockey in the OHL for 2 seasons with the Oshawa Generals. He has formerly played for the Florida Panthers for 3 seasons and the Boston Bruins for 3 seasons. During his time with the Bruins, Horton won the Stanley Cup with them on June 15, 2011 when the Bruins defeated the Vancouver Canucks in game 7 by a score of 4-0. On July 5, 2013, Horton agreed to terms on a seven-year contract with the Columbus Blue Jackets.