Polling stations will close at 4pm BST, with exit poll results expected at 8pm.
This election has seen Macron's centrist government face off against strong opposition from both the left and far-right, highlighting France's increasingly polarised political landscape.
"The country is facing three radically opposed views of society," said Olivier Grisal, a retiree, as he walked towards his polling site in the middle-class town of Conflans Sainte-Honorine, west of Paris, with his wife.
Opinion polls forecast Marine Le Pen's RN will emerge the dominant force as voters punish Macron over a cost of living crisis and being out of touch with the hardships people face.
However, the RN is seen failing to reach the 289-seat target that would outright hand Le Pen's 28-year-old Jordan Bardella the prime minister's job with a working majority.
The far right's projected margin of victory has narrowed since Macron's centrist Together alliance and the left-wing New Popular Front (NPF) pulled scores of candidates from three-way races in the second round in a bid to unify the anti-RN vote.
"France is on the cliff-edge and we don't know if we're going to jump," Raphael Glucksmann, a member of the European Parliament who led France's leftist ticket in last month's European vote, told France Inter radio last week.
