Villepin, a career diplomat, served as French prime minister from 31 May 2005 to 17 May 2007. He gained a fame by slashing the U.S. invasion to Iraq in 2003 during his tenure of French Foreign Minister.
Villepin and Sarkozy have been long-time rivals since they were premier and minister of the Chirac's government. Their rift was highlighted during the Clearstream trial early this year.
In January, after the Paris court cleared Villepin of the charge that he tried to sabotage Sarkozy's presidential bid by smear him in the Clearstream case, the public prosecutors have filed appeal against the verdict, insisting Villepin's sin, which was interpreted as Sarkozy's "vendetta" against the old enemy.
Latest polls showed that Villepin only gained 8 percent of national support as 2012 presidential candidate but 49 percent of approval rate, while Sarkozy's approval rate has declined to history low of 33 percent.