Justyn Warner is a two-time bronze medallist at the IAAF World Championships as a member of the 4x100m relay team in 2013 and 2015. Warner competed in his first Olympic Games in 2012 and placed 13th overall in the 100m. He was also part of the 4x100m relay team with Jared Connaughton, Oluseyi Smith, and Gavin Smellie. The group finished in bronze medal position, but was later disqualified due to a lane violation.
Warner was crowned 2012 Canadian champion in the 100m. He finished sixth as a member of the 4x100m relay team at the 2011 World Championships in Korea and reached the semifinal in the 100m. Warner also represented Canada at the 2005 Pan American Junior Championships, winning silver in the 100m. His younger brother Ian was the alternate on the 4x100m relay team in London.