French President Nicolas Sarkozy's centre-right party won a comfortable majority in parliamentary elections.
Segolene Royal announced that she and her partner are splitting
But his UMP party fell far short of the landslide win predicted for it in the second-round vote, with the Socialist opposition faring better than expected.
The UMP won 314 seats in the 577-member assembly, while the Socialists won 185. Voter turnout was low, at about 60%.
The results will be seen as a minor setback for Mr Sarkozy's party, says the BBC's Caroline Wyatt in Paris.
However, a major blow for the UMP was the defeat of former Prime Minister Alain Juppe, who was made energy and environment minister in the new government after Mr Sarkozy's election.
Mr Juppe said he would offer his resignation. Mr Sarkozy has insisted that any minister would have to leave the government if they failed to be elected.
But the victory gives Mr Sarkozy enough room to start pushing his reforms through parliament, our correspondent says.
Mr Sarkozy has promised to give universities more autonomy, impose tougher sentences on repeat offenders, tighten immigration, make labour laws more flexible and reduce taxation.
The UMP and its allies' 314-seat majority is smaller than the 359 seats they held in the previous parliament, when Jacques Chirac was president.
Former Prime Minister Alain Juppe, appointed to be energy and environment minister in new government
Marine Le Pen, daughter of far-right National Front leader Jean Marie le Pen
Jean-Louis Bruguiere, France's best known anti-terrorist judge, standing for UMP
The Socialists and their allies won 185 seats, up from 149 in the previous assembly.
The centrist Democratic Movement, founded by presidential candidate Francois Bayrou, won three seats. The far-right National Front party did not win any seats.
French Prime Minister Francois Fillon said the result gave Mr Sarkozy a strong mandate to introduce his reforms.
"Your participation has resulted in a clear and coherent choice, which will allow the president of the Republic to implement his project," he said.
The leader of the Socialists, Francois Hollande, said the result was "good for the country".
"The blue wave that had been predicted... has not taken place. In the new assembly, there will be diversity and pluralism," he said.
He also described the result as an indictment of "unfair measures" set to be introduced by the UMP such as raising sales taxes from 19.5% to 24.5% to finance healthcare costs.
The Socialists' results are a relief to the party, which has been riven by infighting since its candidate, Segolene Royal, lost the presidential elections in May.
But according to our correspondent, discussion on Monday is likely to focus on a surprise announcement by Ms Royal that she is splitting from her partner, the Socialists' leader, Francois Hollande.
The defeated presidential candidate said in a book to be published this week that her partner was having an affair.
"I have asked Francois Hollande to leave our home, to pursue his love interest which is now laid out in books and newspapers and I wish him happiness," she said in an interview ahead of the book's release on Wednesday.
The couple have been together for more than 25 years and have four children.
Ms Royal has said she will challenge Mr Hollande for the party's leadership.