Turnout was markedly down, reflecting a sense of resignation among Macron's opponents faced with polls showing the 39-year-old set to sweep the board, buoyed by a deep desire for political renewal.
Prime Minister Edouard Philippe said that despite an abstention rate estimated at just over 50 per cent, "the message of the French people is unambiguous".
Parisian voter Thibault Gouache said he was keen to see fresh faces in the parliament.
Marine Le Pen's Front National won 14 per cent of the vote, according to Ipsos.
In the wake of Le Pen's qualification for the presidential runoff, her far-right National Front party is expected to get its highest-ever score, but doesn't appear able to become the major opposition force Le Pen had hoped for.
She also slammed the electoral system as unfavorable to smaller parties like hers.
Mounir Mahjoubi, junior minister in charge of digital affairs, said on BFM television that voters have acknowledged that the first weeks of Mr Macron's presidency "have been exemplary" and "have allowed the French to see there is a path that suits them".
While an Elabe poll projects 32 percent for Macron's party and its center-right Modem ally, it further says that conservative Republicans and their allies received nearly 21 percent of the votes.
The party secured a crushing 32.2 per cent of the vote, which the Ipsos poll projected would give En Marche between 390 and 430 of the 577 seats in France's lower house.
Far-left leader Jean-Luc Melenchon, who came in a strong fourth place in the presidential vote with almost 20 percent support, is running for a parliamentary seat in the southern city of Marseille.
Polling agencies project that Mr Macron's party will win a large majority in the second round June 18.
The two mainstream parties that dominated French politics for decades were again left licking their wounds, marginalised by the swing of voter support behind Mr Macron's political revolution.
The projections from Sunday's voting show Macron's Republic on the Move movement is in strong position to win the decisive second round vote June 18.
On the right, the conservative Republicans were also reeling, projected to end up with possibly no more than 110 seats, and possibly as few as 70, having controlled 215 in the outgoing parliament.
The record-low turnout, however, took some shine off the achievement for En Marche - a fledgling party fighting its first-ever election and dedicated to providing France's youngest-ever president with the legislative majority he needs to be effective and enact his promised programme of far-reaching change for France.
Some 19.24 percent of voters had cast ballots by midday (1000 GMT), the interior ministry said, compared with 21.06 percent at the same time of day in the first round of 2012.
His fledgling Republic on the Move! - contesting its first-ever election and fielding many candidates with no political experience at all - was on course to deliver him a legislative majority so crushing that Macron's rivals fretted that the 39-year-old president will be able to govern France nearly unopposed for his full five-year term.