The son of a doctor and an insurance salesman started playing tennis at the age of six. In 2002 he became a professional. In 2004 in Metz, Simon made his debut on the ATP World Tour . In 2005 he reached the quarter-finals in Casablanca and was in the main draw of a Grand Slam tournament for the first time at the French Open , when he lost to his compatriot Olivier Patience in the first round .
Simon won his first ATP tournament in Marseille in 2007, and on March 19, 2007 he was ranked 38th in the world . In the same year he reached the second round at the French Open and Wimbledon .
In 2008 Simon made his breakthrough. At the Masters in Cincinnati , he defeated the then world number one Roger Federer . In the semifinals he then had to admit defeat to Nicolas Kiefer . At the US Open he was defeated in the third round to the Argentine Juan Martín del Potro . After defeating the Spanish "oldie" Carlos Moyá in the final in Bucharest , Simon climbed to 13th place in the world rankings for the first time.
In 2009 he started at the Australian Open as number 6 on the seeding list and reached the quarter-finals, in which he was eliminated against the eventual tournament winner Rafael Nadal with 2: 6, 5: 7, 5: 7. The French Open ended for him with a 4: 6, 4: 6, 2: 6 against the Romanian Victor Hănescu in the third round. In Wimbledon he defeated Victor Hănescu and reached the round of 16, in which he had to admit defeat to Juan Carlos Ferrero, who was playing with a wild card in the main draw .
After he failed in the third round of the US Open against world number one Rafael Nadal , Simon won his seventh ATP title in Metz in September 2010 .
He started 2011 with his eighth ATP title in Sydney . At the Australian Open he was eliminated in the second round with 2: 6, 3: 6, 6: 4, 6: 4, 3: 6 against Roger Federer; so he received his first defeat in the third encounter against the Swiss. This was followed by the ninth ATP title in Hamburg and thus the first at a tournament in the ATP World Tour 500 category .