The National Front is expected to win only a handful of seats despite its third-place showing in the first round. Melenchon, whose party was projected to win 25 to 30 seats, denounced Macron's planned labor reforms that would make it easier to hire and fire French workers, calling them a "social coup d'etat" that he would fight.
Le Pen's defeat, as well as her poor performance in the presidential debate against Macron and an internal party controversy over whether to continue to defend a French exit from the euro, have demobilised FN voters during the legislative campaign.
Macron drafted a piece of legislation, according to TheNYT, "that would permanently legalize much of the state of emergency instituted by President Francois Hollande shortly after the terrorist attacks in Paris in November 2015".
Just months ago, Macron was given little chance of becoming president, never mind dominating parliament, but he and the movement he founded 16 months ago have tapped into widespread desire for wholesale change. Sunday's vote was overshadowed by low voter turnout and widespread disillusionment with politics.
French voters were expected to hand his year-old Republic on the Move party an overwhelming majority.
"You can not leave the prospects for the assembly as they stand - our country needs an opposition to function", National Front leader Marine Le Pen has warned.
It is the second-round of the election featuring run-off contests between the top candidates after the first round held last Sunday.
Centrist La Republique en Marche party (REM), founded by President Emmanuel Macron, came in first with 28.21 percent of the votes.
Pollsters predict the party faces financial ruin with its strength in parliament falling from almost 300 seats to around 20 after their five years in power under president Francois Hollande.
Polls show Macron is on course to win the biggest parliamentary majority since de Gaulle's own conservatives in 1968.
The National Front had two seats in the outgoing parliament and the only lawmaker seeking to renew his mandate, Gilbert Collard running in the southern Gard region, could lose.
The Interior Ministry said the midday participating figures in Sunday's nationwide voting compare to 21.4 percent at midday during the second round of the last parliamentary elections in 2012.
The traditional rightwing Republicans, which most polls suggested would win the presidential and parliamentary elections only six months ago, are tipped for 60-132 seats from more than 200 now.
Should LREM manage to secure the majority it's predicted to on Sunday, this would allow Macron to easily confirm his government, headed by Prime Minister Edouard Philippe.
Jean-Luc Mélenchon's far-left party will likely claim between 10-20 seats after accounting for 11% of the vote in the first round.