Ongaro won his first cap in 2000 when the Azzurri played against Canada in Rovigo, in a 17–22 loss. Ongaro played every match for Italy in the 2003 World Cup. He scored the crucial try that helped beat Scotland 20–14 in Rome in the 2004 Six Nations Championship. His rise to the top peaked in November 2004 when he was named as Italy captain in place of the injured Marco Bortolami. He played 2 matches at the 2007 Rugby World Cup. He has been a regular player at the Six Nations since 2003.