The result, if confirmed, redraws France's political landscape, humiliating the traditional Socialist and conservative parties that alternated in power for decades until Macron's election in May blew apart the left-right divide.
Two pollsters projected that Macron's Republic on the Move (LREM) and its Modem allies would win 355-360 seats in the 577-seat lower house, lower than previously forecast.
A third poll by Elabe showed a far bigger majority, projecting 395-425 seats from the Macron alliance.
The three projections predicted the conservative The Republicans and its allies would form the largest opposition block with 97-133 seats while the Socialist Party, in power for the last five years, and its partners would secure 29-49 seats, their lowest ever.
Marine Le Pen, Macron's arch-rival on the far right, may get four to eight seats, they said.
The scale of the majority hands Macron, a pro-European Union centrist, a strong platform from which to make good on campaign promises to revive France's fortunes by cleaning up politics and relaxing regulations that investors say shackle the euro zone's second-biggest economy.
Voter turnout was projected to be a record low for parliamentary elections in the post-war Fifth Republic at about 42 percent.
France's youngest leader since Napoleon, Macron emerged from relative obscurity to score a thumping win in the presidential election in May.
Having never held elected office, he seized upon the growing resentment towards a political elite perceived as out of touch, and on public frustration at their failure to create jobs and spur stronger growth to win the Elysee.
His year-old party then filled the political space created by the disarray within the Socialist Party and The Republicans, with Sunday night capping a sequence of events that a year ago looked improbable.
Moreover, the scale of LREM's win means Macron will enjoy an absolute majority even without the support of alliance partner Francois Bayrou and Modem, lending him a freer hand for reforms and room for a government reshuffle should he chose. Modem currently has two ministers in the cabinet.
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