The Socialist Party of France's President Francois Hollande has won enough seats in parliament to form an absolute majority, according to exit polls obtained by the AFP news agency.
The exit polls suggested the party and its allies would take more than 312 out of 577 seats in the National Assembly.
If confirmed, it means the Socialists will not have to rely on support from either the Greens or the far-left.
It gives the president strong backing as he seeks measures to boost growth.
Mr Hollande has promised to hire more public workers and to refocus EU fiscal efforts away from their emphasis on austerity.
The vote was the second round of a two-part parliamentary election.
The polls suggested the conservative UMP party and its allies would win between 212 and 234 seats, and the far-right National Front between one and four seats.