With slightly higher-than-expected voter turnout, pollsters were predicting a "red wave" across the country that would give President Francois Hollande's Socialist Party and its allies a majority in the lower house of parliament.
The first round of voting last Sunday saw a record 42.8% abstention rate, but voters appear to have heeded calls from both sides of the political spectrum to cast their ballots this week.
If the Socialists achieve a parliamentary majority, either alone or in conjunction with the Green Party and the Left Front, the recently elected Hollande and the French left would have more power than any other administration in modern France. The Socialist Party already controls the upper house of parliament, the Senate, as well as a majority of regions and the main French cities.
In last week's first round, 36 candidates won seats outright with a majority of votes -- 25 from the left and 11 from the right, leaving 541 seats up for grabs. Overall, the left garnered 45.7% of the vote versus 34.1% for the right.
In Sunday's runoff, all eyes were on the coastal constituency of La Rochelle in western France, where Hollande's former partner and the mother of his four children, Segolene Royal, faced a challenge from a Socialist Party dissident. In what was characterized as a fit of jealousy, Hollande's current companion, journalist Valerie Trierweiler, caused a storm last week after tweeting her support for Royal's rival in defiance of the president and his party.
The far-right National Front is also hoping to win its first seats in parliament in 24 years. Among its best hopes are party leader Marine Le Pen, who is standing for election in France's northern industrial heartland, and her 22-year-old niece Marion Marechal Le Pen, who is expected to win in her Provence constituency. Pollsters predict the National Front will win three seats at most.
The polls close at 8 p.m. French time, when early exit polls will offer the first clue as to whether the Socialists have secured the 289 seats needed for an absolute majority.
"There's everything to play for. Previous legislative elections have proven that numerous seats can be decided by a few dozen votes," Prime Minister Jean-Marc Ayrault told journalists last week.
-- Kim Willsher
Photo: Residents of the northern French town of Henin-Beaumont vote in parliamentary elections. Credit: Philippe Huguen / Agence France-Presse/Getty Images