French President Jacques Chirac has said he will support the centre-right candidate, Nicolas Sarkozy, in his bid for the presidency.
Mr Sarkozy has sought to distance himself from the president's legacy
Mr Sarkozy, the current interior minister, has had sharp differences in the past with Mr Chirac, who is stepping down after 12 years in office.
Mr Chirac also announced Mr Sarkozy would be leaving the government on 26 March to focus on the race.
The first round of polling takes place on 22 April.
Mr Chirac announced he would give his "vote and support" to Mr Sarkozy in a televised statement at the Elysee presidential palace.
He said that as Mr Sarkozy's bid had received the full backing of the ruling UMP party, it was "totally natural that I give him my vote and my support", he said.
Latest polls show Mr Sarkozy leading the race ahead of the Socialist Segolene Royal and the centrist Francois Bayrou.
Far-right leader Jean-Marie Le Pen comes fourth, well ahead of the eight remaining candidates.
Several months after Mr Sarkozy's nomination, Jacques Chirac has at last, belatedly, given his blessing to the candidate after the two men met in private on Monday, says the BBC's Caroline Wyatt in Paris.
But that could be a double-edged sword as Mr Chirac is one of France's least popular presidents after 12 years in power, our correspondent adds.
President Chirac and Nicolas Sarkozy have long had a stormy relationship.
Once close political allies, the young Mr Sarkozy was a protege of Mr Chirac's until he backed a rival candidate for the 1995 elections, only to see Mr Chirac gain power.
Since then, the two have had an uneasy rapport with mutual admiration mingled with suspicion.
Their relationship became even more prickly after the ambitious Mr Sarkozy took over President Chirac's political party, the UMP, and turned it into his own election machine.
Though Mr Sarkozy has long been a leading member of his government as finance and later interior minister, he has often sought to distance himself from his former mentor, seeing Mr Chirac's support as a potential liability for these elections.