Centre-right candidate Nicolas Sarkozy will face Socialist Segolene Royal in the run-off of France's presidential election on 6 May.
Voters now faced a clear choice, Mr Sarkozy told supporters
With all the votes counted in Sunday's first round, Mr Sarkozy had 31%. Ms Royal, bidding to be France's first woman leader, got nearly 26%.
Centrist Francois Bayrou had 18%, and far-right Jean-Marie Le Pen almost 11%.
Voting reached near-record levels, with turnout put at almost 85% - the highest for nearly 50 years.
Disillusionment with politicians and their promises did not translate into apathy, reports the BBC's Caroline Wyatt in Paris.
Instead, young and old alike queued at the polling booths at schools and town halls, although in their choices they remained as divided as ever.
Voters turned out in such high numbers that the authorities decided to allow more time for people who were still queueing.
Of the main candidates, Mr Sarkozy, a former interior minister, promised a "rupture" with the past and real economic reform, while Ms Royal has pledged a fairer society.
Both are controversial figures who have divided the French.
Mr Sarkozy is hated by the left as a reformer who many fear would change the French way of life by making the nation work harder and longer and by cutting back on its generous welfare state.
Ms Royal is also regarded with suspicion, seen as too authoritarian and conservative by some Socialists.
Addressing a cheering crowd at his election headquarters, Mr Sarkozy said France had chosen to have a real debate between two different types of politics.
"The debate should be a real debate of ideas," he said.
He went on to appeal to all voters, saying: "I invite all French people, whatever their origin, whatever their beliefs, whatever their party to unite with me."
Ms Royal also stressed that voters now had a clear choice on 6 May.
She represented those who wanted to "reform France without brutalising it", she told supporters.
"You have given me the responsibility of continuing the fight for change in order that France rises up."
The centrist Francois Bayrou, who said he would bring together left and right in a government of national unity, failed to capitalise on early hopes.
NEXT STAGE OF ELECTION
27 April: Campaigning restarts
2 May: Televised debate
6 May: Second round poll
10 May: Final official results
But Mr Sarkozy and Ms Royal will be bidding to win over the political centre that he energised well enough to turn the election briefly into a three-way race.
Several million French people had opted for change, Mr Bayrou told his supporters.
"From this evening, French politics have changed and will never be as before," he said.
Observers said it was a disappointing result for 78-year-old Mr Le Pen - whose prediction that he would win through to the second round, as he did in 2002, failed to materialise.
The far-right leader has, however, seen many of his ideas on patriotism and immigration filter into the mainstream campaigns.
Mr Le Pen blamed the media for his defeat and said he would announce on 1 May his position for the second round.
Together Mr Bayrou and Mr Le Pen accounted for some 30% of the votes. Six other left-wing candidates won a total of about 10%, while two other conservative candidates together picked up more than 3.5% of the vote.