Lawmakers held a special session at the Chateau de Versailles
Parliamentarians in France have approved plans by President Nicolas Sarkozy to rewrite the constitution - by the slimmest of margins.
The bill was backed by 539 votes to 357 - one vote more than the three-fifths majority of the combined Assembly and Senate required to pass the reforms.
The reforms will strengthen France's parliament, Mr Sarkozy says, by allowing it to set half its agenda.
It also limits the president to two five-year terms in office.
But the opposition says the reforms will turn the country into a "monocracy". Socialists suggest the new bill will be the equivalent of crowning Mr Sarkozy king.
"While we were hoping for progress for democracy, you are offering us consolidation of 'monocracy'," Socialist senator Bernard Frimat told lawmakers before the vote at a special session at the Chateau of Versailles.
The reform bill represents the biggest shake-up in the way France is run since the constitution was introduced by Charles de Gaulle in 1958, observers say.
The vote is a victory for President Sarkozy who made overhauling France's Constitution one of his key election pledges, the BBC's Emma Jane Kirby in Paris says.
'Movement, change, modernity'
Mr Sarkozy, while on a trip to Dublin to discuss the future of the EU's Lisbon Treaty, hailed the news that his reforms had passed.
President Sarkozy said he was "absolutely delighted" by the outcome
"It is French democracy that has won," he said.
"The camp of movement, change, modernity has won over the camp of immobility, of rigidity, of sectarianism."
The most contentious part of the bill has been a plan to allow the president to address parliament, opening up the possibility of a US State of the Union-style address.
That has not been permitted since 1875, in an attempt to keep the executive and legislative branches separate.
Mr Sarkozy, however, says the measures will actually strengthen parliament and make the president more accountable.
The bill sets a two-term limit for presidents, gives parliament a veto over some presidential appointments, ends government control over parliament's committee system, allows parliament to set its own agenda, and ends the president's right of collective pardon.
The bill was dependent on cross-party support, leaving the outcome unclear right up to the vote.
Mr Sarkozy spent the weekend on a break with his wife Carla Bruni in Morocco, but was reported to have been calling France frequently to try to consolidate support for the moves.
Last-minute concessions failed to win the support of the opposition Socialists, the Greens and the Communists, who all said they would vote against.
Nevertheless, the bill achieved the 538 votes needed, with one to spare.