Halák has represented Slovakia internationally on multiple occasions. He first played for his country at the IIHF World U20 Championship, starting every game for the team in both the 2004 and 2005 tournaments, where the team finished sixth and seventh, respectively. Halák's first senior international experience came in 2007 as he played in the 2007 Men's World Ice Hockey Championships, starting 2 games and earning a 1–1 record. The Slovaks finished in sixth place. Halák again represented Slovakia at the 2009 tournament, where the team finished 10th overall.