Tatar represented Slovakia at the 2009 World Junior Ice Hockey Championships, where he was the team's leading-scorer, and finished tied for fourth in tournament scoring, recording seven goals and four assists in seven games. Tatar again represented Slovakia at the 2010 World Junior Ice Hockey Championships, where he scored three goals and two assists in six games. That same year, he also represented the senior Slovak team at the 2010 IIHF World Championship, scoring two goals in six games.