Jefferis represented Australia at the 2002, 2006 and 2010 Commonwealth Games. At the 2006 Commonwealth Games, he earned a gold medal in the men's all around event, a gold medal in the rings, and a silver medal in the team competition. At the 2010 Commonwealth Games, he helped Australia win their first gold medal in the men's team event, and took an individual gold on the parallel bars and bronze in the all around event. He competed in the World Championships in 2003, 2005, 2006, 2007, 2010, and 2011. At the 2003 Championships, he was the youngest member of the Australian all around team. His best performance at Worlds was twelfth place in the all around competition in 2006.