EELV's former leader in the Senate, Jean-Vincent Placé, and one of its former vice-chairs in the National Assembly, François de Rugy, officially announced the launch of Ecologistes!, their new party, on Saturday.
They have been joined by the other National Assembly vice-chair, Barbara Pompili, and another MP, Véronique Massoneau.
"I hope this new party will be more open to tolerance and listening to people" than EELV, Placé told the media. "Ecology as represented by EELV gives the impression of being churlish and dogmatic."
About 350 people attended the party's opening meeting, according to the organisers.
The new party's leaders accuse EELV of ultra-leftism, following the party's departure from the government last year and its alliance with the hard-left Left Front in some parts of the country for the regional elections.
Calling for a "pragmatic, realistic and positive ecology", Placé said the Ecologistes! are discussing with the Socialist Party about presenting joint tickets in the December polls "all over the country".