Halenár played at two youth tournaments for his country, the UEFA European Under-19 Championship in 2002 and the Under-20 FIFA World Youth Championship in 2003. On 13 November 2007, he made his debut for Slovakia's senior team in a qualifying game for the 2008 European Championship against the Czech Republic. Halenár also played in next two matches of the national team, when he came on as a substitute against San Marino and Hungary.