© REUTERS/Eric Feferberg/Pool
The two went into the debate with opinion polls showing Macron, 39, maintaining a strong lead of 20 percentage points over the National Front's Le Pen, 48, in what is widely seen as France's most important election in decades.
For Le Pen, the debate, watched by millions, was a last major chance to persuade voters of the merits of her program which includes cracking down on illegal immigration and ditching the euro currency.
In angry exchanges, Le Pen played up Macron's background as a former investment banker and economy minister, painting him as a continuation of the outgoing unpopular Socialist government and a backer of rampant globalization. He accused her of not offering solutions to problems such as France's chronic unemployment.
But the sharpest exchange was over national security, a sensitive issue in a country where more than 230 people have been killed by Islamist militants since 2015.
Le Pen accused Macron of being complacent in confronting the threat of Islamist fundamentalism. "You have no plan (on security) but you are indulgent with Islamist fundamentalism," she said.
Macron retorted that terrorism would be his priority if he is elected and accused Le Pen of being simplistic. "What you are proposing is snake oil," he said, referring to her proposals to close France's borders.
"I will lead a fight against Islamist terrorism at every level. But what they are wanting, the trap they are holding out for us, is the one that you offer - civil war," he said..
"GLOBALIZATION GONE WILD"
Le Pen labeled Macron a "smirking banker" and said he represented unfettered globalization.
"Mr. Macron is the candidate of globalization gone wild, of Uberisation, of precariousness, of social brutality, of war by everybody against everybody ... of the butchering of France by big economic interests," she said, referring to the gig economy typified by U.S. app-based cab service Uber.
Macron hit back by calling Le Pen a liar, saying she was talking nonsense and that her rhetoric lacked substance.
On unemployment, Macron told Le Pen: "Your strategy is simply to tell a lot of lies and just to say what isn't going right in the country."
The two candidates, seated opposite one another at a table in the television studios, mapped out diametrically opposed visions for France. Macron calls for liberal reforms to kickstart the French economy, while Le Pen rails against the loss of French jobs through off-shoring and would adopt protectionist trade measures.
Macron finished only three points ahead of Le Pen in the first round on April 23, but he is widely expected now to pick up the bulk of votes from the Socialists and the centre-right whose candidates were eliminated.
Though Le Pen has a mountain to climb, the campaign has been packed with surprises.
Upwards of 20 million viewers out of an electorate of close to 47 million were expected to tune in to the two-and-a-half hour debate.
In an interview with Reuters on Tuesday Le Pen reaffirmed she wanted to take France out of the euro and get a national currency back into French pockets within two years.
ABSTAINERS TARGETED
Wednesday's event marks the first time a National Front candidate has appeared in a run-off debate - an indication of the degree of acceptance Le Pen has secured for the once-pariah party by softening its image in an attempt to dissociate it from past xenophobic associations.
Outgoing President Hollande, hours before the two rivals sat down before the cameras, renewed a call to stop Le Pen and vote for Macron.
A Cevipof poll published on the website of Le Monde on Wednesday - one of the last big surveys before Sunday's vote - saw Macron getting 59 percent of votes versus 41 percent for Le Pen. An Ifop-Fiducial poll for Paris Match, CNews and Sud Radio gave Macron a 60-40 lead.
His camp meanwhile said that, if elected, he might put back a deadline for cutting back reliance on nuclear power in the French energy mix - an announcement that sent EDF shares up 4.9 percent in heavy trade.
Assuming he wins, one of Macron's immediate tasks will be to build a parliamentary majority in follow-up elections in June to push through his program.
He heads only a fledgling movement called En Marche! (Onwards!) which has no representation in parliament.
A poll for Les Echos newspaper by OpinionWay-SLPV Analytics suggested Macron was rising to that challenge, showing his party set to emerge as the largest with between 249 and 286 seats in the 577-seat lower house, while the National Front was tipped to win 15 to 25.
Not very presidential at all.