Voting stations opened in France at 0600 GMT for the second round of the parliamentary election, just a month after the 39-year-old former banker became the youngest head of state in modern French history.
Turnout, though, could touch record lows, in a sign of voter fatigue after seven months of roller-coaster campaigning and voting, but also of disillusionment and anger with politics that could eventually complicate Macron's reform drive.
Macron's centrist Republic on the Move (LREM) party is barely more than a year old yet pollsters project it will win as many as 75-80 percent of seats in the 577-seat lower house.
Many of its lawmakers will be political novices, something which will change the face of parliament at the expense of the conservative and socialist parties which have ruled France for decades.
One of the challenges for Macron as he sets out to overhaul labour rules, cut tens of thousands of public sector jobs and invest billions of public cash in areas including job training and renewable energy, will be to keep such a diverse and politically raw group of lawmakers united behind him.
"There has never been such a paradox between a high concentration of power and strong tensions and expectations in terms of changes," Laurent Berger, head of France's CFDT union, told the weekly Journal du Dimanche.
"There is no place for euphoria in victory. There is no providential man, no miracle solution".
Key rivals say they expect LREM to win a majority of seats and have been urging voters to make the margin as small as possible, saying that democratic debate could otherwise be stifled.
Opinion polls show that voters, while preparing to hand Macron a crushing majority, are actually hoping for a strong opposition to emerge in parliament.
"We need other parties to have some weight," 54-year-old assembly line worker Veronique Franqueville said on the parking lot of a tumble-dryer factory in the northern town of Amiens. "If he wins it all there will be no debate."
But among those who plan to vote for LREM candidates the mood is very different, with an overwhelming feeling that the Macron needs to be given a strong enough majority to carry out the policies on which he was elected just over a month ago.
"I will vote for the 'En Marche' candidate," said Aurelie, a 25-year-old nurse in Amiens, referring to Macron's party. "If we want the president to be able to do things we need to give him a majority."
The election is set to send shockwaves through the older parties, with their unity, and even survival, at stake.
The conservative The Republicans are expected to be the biggest opposition group in parliament. But polls see them securing no more than 90-95 seats out of 577.
Some Republican lawmakers could create a separate group to back Macron on a case-by-case basis, while others may see a future firmly in the opposition.
The Socialist Party, which ruled France until last month, faces a humiliating defeat which could see them with no more than 25-35 seats.
The election also spells trouble for the far-right National Front (FN), seen with only between one and six seats when earlier it had hoped to secure a "massive" presence in parliament. Its leader, Marine Le Pen, is expected to be among those who will be elected.
Far-left leader Jean-Luc Melenchon is also seen winning a seat in parliament. But polls are unclear if his France Unbowed party will reach the 15-strong threshold required to be able to form a parliamentary group.
Polling stations close at 6:00 p.m. local time (1600 GMT) in small and medium towns and at 8:00 p.m. local time (1800 GMT) in Paris and other big cities. At that time, opinion polls will give an estimate of the outcome and official results will start trickling in.
By Ingrid Melander and Maya Nikolaeva
(Editing by Richard Balmforth and Louise Heavens)
© Thomson Reuters 2017