Barnett won the silver medal in the 200m event at the 2006 World Junior Championships, and also competed at the 2007, 2009, and 2011 World Championships in Athletics, as well as the 2008 Olympic Games without reaching the final. For his silver medal performance at the 2006 World Junior Championships, he was named the 2006 Outstanding Junior Athlete of the Year by Athletics Canada. At the 2007 Pan American Games he won a silver medal in the 4 x 100 metres relay, together with teammates Richard Adu-Bobie, Anson Henry and Jared Connaughton.