French prime minister Manuel Valls has announced his candidacy for next year's presidential election.
Mr Valls will face other contenders in the Socialist primary next month.
"I want to give everything for France," the 54-year-old said in a speech in the Paris suburb of Evry.
He said he will quit his job on Tuesday in order to focus on his presidential bid.
His announcement comes a few days after unpopular president Francois Hollande said he will not run again, in the hope of giving the Socialist party a chance to win in the presidential election with a different candidate.
Mr Valls said he wants to defeat the far-right, led by National Front leader Marine Le Pen, and conservative candidate Francois Fillon.
A centre-leaning Socialist with a tough line on security and immigration, Mr Valls is somewhat more popular than his boss, but their party is in deep disarray over the government's handling of the economy.
He is now considered the favourite for the Socialist primary, but needs to overcome divisions within the party.
"My candidacy is that of conciliation, of reconciliation," Mr Valls promised.
Former economy minister Arnaud Montebourg and former education minister Benoit Hamon, who have joined a group of Socialist rebels opposed to Mr Valls's pro-business policies, have announced their candidacy, alongside other lower-profile candidates.