The pair previously collaborated on one of the segments of portmanteau project Paris je t'aime.
Ossard, producer of past hits including Amelie and Delicatessen, spoke about the new project at a gala screening of Paris je t'aime at Edinburgh's Filmhouse during the 15th French Film Festival UK.
Chomet, who is a patron of the French Film Festival UK, is also writing the new film, and will interrupt production of his next animated feature, The Illusionist, to work on the live-action project.
The new film, as yet untitled, will star Paul Putner and Yolande Moreau, who both starred in Chomet's Paris je t'aime short.
Ossard also said that she will produce a new film about the relationship between Coco Chanel and Igor Stravinsky, to be directed by William Friedkin and starring Marina Hands as Chanel.
The French Film Festival UK continues until May 6.