Mitchell has had a successful career in track sprinting after specialising in the 'standing lap' role of first position in the team sprint. Mitchell burst on the scene as a starter at the 2010 Commonwealth Games and has consistently risen the ranks to be one of the world's fastest from the gate. He has received Gold, Silver and Bronze medals at World Cup events and Silver and Bronze at the World Championship level in the team sprint. As Junior World Champion in 2009, an elite men's world title has eluded him and the New Zealand team. At the 2016 Rio Olympics, he won a silver medal alongside Sam Webster and Eddie Dawkins in the team sprint. Mitchell won a bronze medal at the 2017 UCI Track Cycling World Championships in Hong Kong in the sprint event; the first New Zealander who won a world championship medal in an individual event.