This article is more than
4 year oldEcology, Democracy, Solidarity will be largely formed of seven MPs from La République en Marche (On the Move) and other ex-supporters of the president.
The defecting MPs want to focus on green issues and social inequality.
But their decision leaves Mr Macron's party with 288 seats, one short of a majority in the 577-seat lower house.
French commentators said La République en Marche (LREM) still had the backing of two other political allies, the centrist MoDem as well as Agir from the centre-right, which together make up another 56 seats in the National Assembly.
There is even a chance that the party could regain its absolute majority if another defector who leaves the assembly is replaced by a pro-Macron MP.
The Macron camp has been plagued by a series of defections in recent months, and French media said the seven latest departing MPs had come under intense pressure to stay.
Two MPs who had originally planned to join EDS backed down at the last minute, Le Figaro reported.
The new party is not a major blow to Mr Macron electorally, and allies dismissed the moves as part of the "tribulations of parliamentary life".
But it is further evidence of dissatisfaction among the president's MPs, who were swept into the National Assembly in June 2017, weeks after his whirlwind presidential victory.
President Macron's ratings have dipped during France's coronavirus outbreak, however those of Prime Minister Edouard Philippe have increased.
Members of the new Ecology, Democracy, Solidarity (EDS) group said they had failed to change LREM from the inside and would now take an independent stance, neither allied to the government nor the opposition.
One of new party's best-known figures, Paris mayoral candidate Cédric Villani, told French radio that what was important was that the new party went forward.
"There's been talk of treason and rebels, but this ninth political group is made of free men and women who want to devote their souls and conscience to defending ecology, democracy and solidarity," he told France Inter radio.
Newer articles
<p>The deployment of Kim Jong-un’s troops has added fuel to the growing fire in recent weeks. Now there are claims Vladimir Putin has put them to use.</p>