France follows Italy, Spain and Israel, which all adopted laws against skinny models on catwalks or in advertising campaigns in early 2013.
The measure is part of a wider crackdown on eating disorders backed by President François Hollande's government.
Anyone whose body mass index is below a certain level will not be able to work as a model in France.
And agencies found employing models considered too thin could face fines of up to 75,000 euros and a six-month jail sentence.
Photos that have been digitally manipulated to change a model's physical appearance whill have to indicate that they have done so.
Olivier Véran, the lawmaker behind the bill, said the prospect of such a punishment would help regulate the whole sector.
Not everyone shares that view. Paris is one of the world's fashion capitals. The national union of Modelling Agencies complains the law would affect the competitiveness of French modelling.
The ban follows an amendment, targeting websites that encourage dangerous weight loss, whereby people found guilty of inciting others to “extreme thinness” could face a year in prison and a 10,000 euro fine.
Around 40,000 people suffer from anorexia in France, the vast majority of them women.