Final results released early Monday showed Macron's LREM and MoDem won 32.32 percent of the vote, while the center-right party The Republicans and the far-right National Front of Marine Le Pen garnered 21.56 percent and 13.2 percent, respectively.
Projections by three pollsters of LREM's tally after the second round ranged from 390 to 445 of the assembly's 577 seats - potentially the biggest majority since president Charles De Gaulle's conservatives won more than 80 per cent of seats in 1968.
The final result will be declared in the second round of voting next Sunday.
Conceding the party was facing "unprecedented" losses, PS chief Jean-Christophe Cambadelis appealed to voters to rally behind Mr. Macron's rivals to avoid the President monopolising power.
"Support for our above consensus macro scenario, projecting French GDP to grow by 1.5% this year and 1.8% in 2018, if anything creating upside risks", Barclays said in a research note.
French President Emmanuel Macron looks set to take an overwhelming majority in parliament.
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.
"For the past month, the president has shown confidence, willingness and daring in France and on the worldwide stage", Philippe said, calling the result a vindication of Macron's "winning strategy".
Voter rejection of old-style, established politics - already seen in the April-May two-round presidential vote that handed power to 39-year-old Macron - was again manifest in the legislative vote.
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At the same time, the traditional parties on the left and the right have been weakened, with the Socialists looking particularly feeble.
Mr Macron also plans to quickly pass a law to strengthen security measures - effectively making the state of emergency permanent and another one that he says will put more ethics into French politics.
Under France's election rules, low voter turnout could also see fewer candidates make it through the second round next Sunday.
"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.
By late afternoon, just 41 percent of registered voters on the French mainland had cast ballots.
Some 7,882 candidates are running for 577 seats in the National Assembly in Sunday's first round of the two-stage legislative elections. If the projections of 400 to 440 seats for Macron's camp are confirmed, Macron will have a strong mandate to implement his campaign promises of boosting economy and reducing deficit.
Macron professes to be neither right nor left.