Juan Martin Hernandez made his Test debut for Argentina against Paraguay in 2003 and later on that year he was included in the squad that went to the Rugby World Cup, coming on as a replacement against Australia and starting in the pool games against Namibia and Romania. In 2004, he moved to Stade Francais, helping them to win their domestic league that year as well as making international appearances against France, Ireland, and South Africa. At the end of the 2006 season he was named full back of the year after having a successful season with both Stade Francais and Argentina. Hernandez has the ability to play at fly half, centre, or full back, but he usually prefers to play at fly half. His uncle, Patricio Hernandez, is a former professional footballer who represented Argentina at the 1982 World Cup.