The worst losses, however, were for the Socialists of Mr. Macron's predecessor Francois Hollande, who were shown dropping a staggering 200 seats.
The party and its ally MoDem won 32 per cent of the first round, ahead of the Republicans and its allies on 21.6.
The conservative Republicans had 16 percent, followed by the far-right National Front with 14 percent.
Turnout was much lower than in previous years, down to 48.7 per cent from 57.2 per cent in 2012. "The result shows the wish of the French for coherence and to give a majority to the president of the Republic", said Christophe Castaner, the party spokesman, although he cautioned against complacency for the second round, warning that "nothing can be taken for granted".
Socialist secretary general Jean-Christope Cambadelis warned of an "almost complete lack of real opposition" if LREM's majority was confirmed in the second round of voting.
Another sign of voters' rejection of the political mainstream was that far-left leader Jean-Luc Melenchon was, with the Communist Party, projected to see his camp win as many as 18 seats, an improvement on the 10 they held before.
The prime minister also thanked security services for protecting voting stations and ensuring a safe vote after a string of deadly extremist attacks.
Marine Le Pen, who faced off against Macron in the second round of the presidential race, had hoped her party would go on to become his major opposition in Parliament.
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.
She also slammed the electoral system as unfavorable to smaller parties like hers.
"We had a recent (presidential) election that shook up the traditional parties and I think that the legislative elections give Macron the possibility to show what he is able to do", Fezeau said.
LREM party president Catherine Barbaroux thanked voters because "their choice has a clear meaning: they want the action taken by Emmanuel Macron, since his election to the Presidency of the Republic, to be continued".
The far-right National Front party secured 13.1 percent, and the Socialist Party and a grouping of left-wing parties only managed nine percent.
He called the result a vindication of Macron's "winning strategy".
France's youngest-ever president at 39 coasted to victory in Sunday's first round on the back of a strong debut.
Candidates who win a majority in their constituency will be elected on the first round, as long as they have the votes of at least 25 per cent of registered electors.
The Macron victory is the largest majority in France since Charles de Gaulle's landslide win in 1968.
But Sunday's turnout hit a record low of 49 percent, mirroring the French people's growing disinterest in legislative elections. Less than 50 percent of the 47.5 million electors cast ballots - showing that Macron has limited appeal to many voters.
Some 7,882 candidates are competing for the lower house of parliament's 577 seats.
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