"I have understood that humanity is a strength, not a weakness. I have changed," said Sarkozy in an 80-minute address to a 60,000-strong cheering party from a vast stage bearing the colours of the national flag.
Alfred Grosser, an election analyst in France, said: "He related to his situation as a former immigrant and spoke about Europe with something new – that the treaty is dead."
The speech aimed at easing voter fears, which showed in a poll that he worried 51 per cent of voters, a fact that his political enemies within and outside the ruling UMP party see as his greatest electoral weakness.
Signalling a desire to rise above his partisan past, Sarkozy concluded: "I ask you to understand that I will be the candidate not just of the UMP, that at the moment you have chosen me I must turn towards all the French people.
"I must unite them, I must convince them that together, everything will be possible"
Nicolas Sarkozy, UMP 2007 presidential candidate
"I must unite them, I must convince them that together, everything will be possible," he said, echoing the phrase that is to be his campaign slogan.
Recent polls suggest that Segolene Royal, the Socialist party leader, could beat him in a May 6 election and become France's first woman head of state.
Sarkozy's Paris rally was overshadowed by internal feuding and attacks by Jacques Chirac, the president, and Dominique de Villepin, the prime minister, which fuelled suspicions they were banking on Sarkozy's defeat to recapture control of the party.
De Villepin briefly attended the rally but boycotted Sarkozy's acceptance speech.
Sarkozy's reputation as a free-market supporter has made voters, already anxious about jobs and living standards fear his economic reform plans.
Many blame harsh language on crime-hit housing projects for the 2005 winter riots, the worst in 40 years.