Coombs made his Australian representative debut in 2011 while based in the US when he was selected in the men's coxed four to race at the 2011 U23 World Rowing Championships in Amsterdam. That crew placed seventh overall.[9] He was again picked in the U23 coxed four for the 2013 U23 World Championships when they finished in overall fourth place in Linz, Austria.[9] For the 2014 U23 World Championships in Varese, the entire Australian men's eight was seated with US based Australian rowers and Coombs raced in the six seat of that crew to a silver medal.[9]
In 2017 made the Australian senior squad and was vying for a seat in the men's eight during the European racing season. He
was seated at four in the eight when they finished in 4th place at World Rowing Cup II. Then at WRC III he raced in the coxed pair with Nathan Bowden and James Rook to a silver medal and also in a coxless pair to 13th place. Coombs was back in the Australian men's eight when they finished eight at the 2017 World Rowing Championships. It was his first and last senior Australian representative appearance at World Championships.[9]
