The current frontrunners, far right Marine Le Pen and liberal maverick Emmanuel Macron were joined by conservative, scandal-hit François Fillon, Socialist Benoit Hamon and the far-left wildcard Jean-Luc Melenchon.
A snap opinion poll showed Macron, a 39-year-old former economy minister who has never run for public office before, was the most convincing among the top five contenders in a marathon debate of almost 3½ that delivered no knock-outs.
The anti-immigrant Le Pen, who wants to restrict religious garb in public spaces, said the burkini was a sign of the "rise of radical Islam in our country" and accused Macron of supporting it.
Jean-Marie Le Pen sent tremors through France in 2002 by beating the Socialists to a place in the presidential run-off against conservative Jacques Chirac.
"How do you learn French, dear madam?"
The televised evening debate involved the five candidates who are expected to be the largest vote-getters in the first round of the two-round vote. "When I have something to say, I will say so myself".
The first-round vote is set for April 23; the top two candidates go to a runoff May 7.
Melenchon interrupted Le Pen as she was calling for boosted French-language teaching.
Judge Gorsuch and the corpse flower
Grassley: "I think they want to remind the fact that past year Republicans did not hold a hearing". And they cast his jurisprudence as elevating corporate interests over individual rights.
"You don't leave the euro and the protection afforded by the European Central Bank.for an adventure. that would ruin borrowers and savers alike", Fillon, who presented himself as the most experienced pair of hands, scolded.
"The traditional parties, those who have for decades failed to solve yesterday's problems, won't be able to do it tomorrow either", said Macron, a 39-year-old former economy minister and investment banker who has never run for elected office.
The debate, the first between the five main candidates, may be crucial in helping viewers make up their minds in a French election that has seen major twists and turns.
But with so many voters undecided and polls showing the abstention rate could be higher than ever in France, the level of uncertainty remains high.
Polls show Mr Macron and Ms Le Pen establishing a clear lead in terms of voting intentions in the first round, while Francois Fillon, the one-time front-runner who has been damaged by a financial scandal, has slipped back.
"I completely disagree with Emmanuel Macron who praised the German chancellor when he was in Berlin for (refugee) policies that turned out to be bad policies and which are now criticised by her own allies in Germany", Fillon said in a slap at his centrist rival.
The TV debate was the top trending topic on Twitter in France on Monday before it even started.
Fillon mocked Le Pen when she suggested Brexit had been fantastic for the UK. "It was used before Brexit, it was used before Donald Trump's election", she said, adding that the British economy was growing faster than the European Union and had lower unemployment despite Brexit.