Ellis began his international career with Canada by winning three gold medals in 2008 at the World U17 Hockey Challenge, IIHF World U18 Championship and Ivan Hlinka Memorial Tournament. At the under-20 level, Ellis has made three appearances at the World Junior Championships, winning gold in 2009 and silver in 2010 and 2011. He is the tournament's all-time leading scorer among defencemen and Canada's all-time assists leader. He also won gold with Team Canada at the 2016 World Championships.