With 90 percent of votes accounted for, Macron's La Republique En Marche (REM) and allies had won 31.9 percent support, Interior Ministry results showed.
The conservative Republicans had 16 percent, followed by the far-right National Front with 14 percent.
Record-low turnout, however, took some shine off the achievement.
He has been praised for appointing a balanced cabinet that straddles the left-right divide and taking a leading role in Europe's fight-back against US President Donald Trump on climate change.
The main victim of the vote is the Socialist Party of Macron's predecessor Francois Hollande.
Socialist leader Jean-Christophe Cambadélis lost his seat in the first round.
Cambadelis called on voters to favor more political pluralism in the second round.
While Macron and Merkel have both demonstrated an unwavering commitment to the European Union and Merkel strongly applauded Macron's election, they are likely to differ over Macron's desire for E.U. -issued bonds, a measure Merkel has strongly opposed in the past.
Election officials on June 12 said that with almost all ballots counted, Macron's Republique en Marche party (Republic on the Move) had 28 percent of the vote in an election marked by a historically low turnout.
"The Assembly needs deputies who are genuinely opposed to the political catastrophe Emmanuel Macron is preparing for us", Le Pen said, accusing the president of wanting to "lay waste" to the country's labor code and allow mass immigration.
The right-wing Republican party, which only at the start of this year had seemed on course to win the Presidency under Francois Fillon, will be nearly certainly be the main opposition, with between 70 and 110 seats according to Ipsos projections.
The FN, which has long complained that France's winner-takes-all system discriminates against small parties, is meanwhile forecast to garner only between one and 10 seats.
Murray Downs Nishikori to set up Wawrinka Showdown
On the clay courts of Paris , determined the semifinalists of the 116th version of the Open championship of France. I have worked hard to build my confidence. "Personally I think it was put down to the conditions".
It was not clear how opposition parties would be able to stem much of Macron's advance in Sunday's final round.
The first round of the legislative elections took place on Sunday, with early results on Monday suggesting the new centrist party led by Macron has won 32.32%, ahead of nearest challengers Les Républicains on 21.56% and Marine Le Pen's Front National on 13.20%.
He said that "millions" of voters "confirmed their attachment to the president's project for renewal, gathering and reconquest".
Baroin suggested that voters were so enamored of Macron that they failed to scrutinize his program.
France's youngest-ever president at 39 coasted to victory in Sunday's first round on the back of a strong debut.
France's right wing Republican party, allied with the Union of Democrats and Independents, secured 18.80 percent.
President Emmanuel Macron's new party is set for a landslide victory in the latest round of the French election, allowing him to govern the country nearly unopposed for the next five years.
Macron wants a powerful mandate to push through plans to reduce worker protections to boost hiring, boost security and clean up corruption in politics.
The election was marked by what pollsters predicted would be a record-low turnout of just under 50 per cent.
Such a margin of victory in the 577-seat house would give Macron the majority he so badly craves to further his political revolution. That compared to 48 percent at the same time in the first round five years ago and 49 percent in 2002.
Some 7,882 candidates are running for 577 seats in the National Assembly in Sunday's first round of the two-stage legislative elections. His parliamentary candidates include a historic number of newcomers that from a cross-section of society: from an ex-bullfighter to a former fighter pilot, a mathematician and an anti-corruption magistrate as well as former local politicians - whose key campaign argument was "give the new president a chance".
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