President Francois Hollande's Socialists and their allies are set for a majority following the first round of voting in French parliamentary elections, according to final results.
Left-wing and green parties won a total of more than 46% of the vote compared with 34% for the centre-right UMP party, interior ministry figures showed on Sunday.
The outcome of the polls is expected to determine the extent and pace of reform under the newly-elected French leader. Run-offs are to be held this week, the BBC reports. The turnout nationwide was a modest 57%.
France's 46 million eligible voters have been picking representatives for 577 seats in the National Assembly.
TNS Sofres, Ipos and OpinonWay pollsters agreed that the Socialists and their Green allies might win as few as 283 seats or potentially as many as 347. However, potential allies in the anti-capitalist Left Front would take 13 to 20 seats and ensure a majority.
The communist-backed Left Front, led by Jean-Luc Melenchon, won 6.9% of the vote.
The election also saw a surge in support for Marine Le Pen's far right National Front, which won almost 14% of votes - way beyond the 4% it achieved in the last parliamentary election of 2007.
However, under France's first-past-the-post system, that would give the party only three parliamentary seats at best and possibly none at all.
The BBC reports it is hard to predict accurately what the final tallies will be before this week's decisive round of voting. In many constituencies there will be a three way run-off.
But with the Senate already under the control of the Socialists, it appears that Mr Hollande will also have a majority in the lower house - even if only with the support of allies - which would give him unprecedented power to force through his reform programme.
Mr Hollande's government is due to present a revised budget plan to parliament in July.