The incumbent president sought to overturn a wide poll lag with promises use referendums to consult the French people on controversial reforms such as tightening immigration and overhauling France's generous unemployment benefit regime.
"Yes I am a candidate for the presidential election," he told TF1 channel's evening news programme, saying a "strong France" would protect people from global economic turmoil.
"France is a shield for every one of us. If France is strong, if it takes the decisions, if it makes the choices that will instal it in this new world … then it will be strong. If France is weak, then the French people will be exposed," said the French president.
Polls not optimistic for outgoing president
Dozens of polls show the socialist candidate François Hollande would beat Sarkozy by up to 15 points in a 6 May runoff, but the president's allies hope his dynamic campaigning style will allow him to narrow the gap before a 22 April first round.
Despite a disapproval rating of 68%, Sarkozy hopes to present himself as an experienced leader who can drag France out of an economic slump and overcome the eurozone crisis.
"If you want to make me say I haven't achieved everything, that is for sure. I don't know anyone who has succeeded in everything," Sarkozy said. It was the nearest he came to apologising for the unfulfilled promises of his five-year term.
"What sort of campaign will I run? I will try to tell the truth. To ask the right questions and to offer strong ideas and say to the French 'choose now'."
With unemployment stuck at a 12-year high of 9.3% and a stream of news about companies closing or relocating production abroad, Sarkozy – who took office in 2007 pledging a return to full employment – said he would focus on retraining the unemployed to get them back to work.
After being accused of not listening to popular discontent over pension reforms and tax measures, Sarkozy pledged to consult voters on his reform programme if re-elected.
"The central idea of my programme is to give power back to the French people via the referendum," Sarkozy said.
Sarkozy said economic data released on Wednesday showed his reforms were starting to work. Preliminary data from the INSEE statistics office showed that French gross domestic product (GDP) eked out 0.2% growth in the fourth quarter.
It was the first time since the beginning of 2009 that French quarterly growth outperformed neighbouring Germany, which Sarkozy has repeatedly held up as the economic model to follow.
Apart from the reference to Germany, Europe was otherwise almost absent from Sarkozy's interview, being mentioned only four times by the president, mostly as a background reference to the economic crisis. But he did not develop in any detail his intentions on ongoing European issues, for example on efforts to forge closer economic ties in the eurozone.
On one occasion, Sarkozy referred to the 2005 referendum on the European constitution, saying there is "a France that doesn't believe in anything anymore" and tends to "say no" every time it is being asked.
A 'non-event' for the Socialists
In the past weeks, Sarkozy has announced a 1.6% VAT sales tax increase to fund a cut in payroll charges to improve French firms' competitiveness and he is introducing a 0.1% tax on financial transactions.
He is expected to flesh out his campaign platform in a keynote speech in the Mediterranean port city of Marseille on Sunday. A formidable campaigner, he will hold his first rally on Thursday in the Alpine town of Annecy.
Sarkozy's announcement coincided with Hollande's second major campaign speech on Wednesday in his home city of Rouen.
'Small chance of winning'
A Harris Interactive poll of first-round voting intentions, published on Wednesday, showed Hollande and Sarkozy each gaining one point at 28% and 24% respectively, with three other candidates trailing. In the run-off second round on May 6, Hollande would beat Sarkozy 57% to 43%.
Polling analysts say that with just nine weeks to go, Sarkozy will have a hard time to make up so much lost ground.
"Sarkozy still has a small change of winning if he manages to pull the Socialist candidate into his issues of immigration and security, and as long as the debate does not focus on his personality or achievements," Harris Interactive polling chief Jean-Daniel Lévy told Reuters.
Sarkozy and Hollande both say their priority is to restore public finances and whoever becomes the next president will have to push through roughly €100 billion of austerity measures in the next five years to plug the state deficit.
But they propose very different ways to reach that goal.
Hollande kicked off his campaign in late January with an economic programme that would raise taxes on banks, big firms and the wealthy to help him reduce the public deficit while pumping more funds into education and state-aided job creation.