Michalak made his debut for Toulouse in 1998. He was a member of the team that won the French championship in 2001 and the Heineken Cup in 2003 and 2005. Michalak made his first appearance for France against South Africa on 10 November 2001 and became a regular on the French side. He was selected as a member of the squad for the 2003 Rugby World Cup in Australia and the 2007 Rugby World Cup in France. Michalak was also a part of the Six Nations French Grand Slam winners in 2004 and the champions of 2006.