Nicolas Sarkozy has stepped down as France's interior minister to focus on his presidential candidacy.
Latest polls show Mr Sarkozy ahead
Mr Sarkozy, who is running for the ruling UMP conservative party, was replaced by Francois Baroin, previously minister for overseas territories.
Recent polls show Mr Sarkozy, 52, with a narrow lead over Socialist Segolene Royal and centrist candidate Francois Bayrou in the presidential race.
Twelve candidates are standing in the first round on 22 April.
French President Jacques Chirac, who is stepping down after 12 years in office, last week gave his support to Mr Sarkozy's candidacy.
He said Mr Sarkozy's bid had received the full backing of the UMP party so it was "totally natural that I give him my vote and my support".
Mr Sarkozy has long been a leading member of Mr Chirac's government as finance and later interior minister but has often sought to distance himself from his former mentor.
Opinion polls in the last few days have suggested a 5% gap between the three leading candidates in the first round.
An opinion poll released by the Ipsos agency for Le Point news weekly on Sunday suggested Mr Sarkozy could take 30% of the vote on 22 April.
It put Ms Royal on 25.5% and Mr Bayrou on 19%.
The election is expected to go to a second round runoff between two candidates on 6 May.