Forain's quick and often biting wit allowed him to befriend poets Arthur Rimbaud and Paul Verlaine as well as many writers, most notably Joris-Karl Huysmans.

[1] He was the youngest artist to frequent and participate in the feverish debates led by Édouard Manet and Edgar Degas at the Café de la Nouvelle Athènes in Montmartre.

Influenced by Impressionist theories on light and color, he depicted scenes of everyday life: his watercolors, pastels and paintings focused on Parisian popular entertainments and themes of modernity—the racetrack, the ballet, the comic opera and bustling cafés.

In 1892 he published the first volume of La Comédie Parisienne, a collection of Forain's illustrations and commentary on the major political stories that disrupted France's Third Republic—such as the anarchic crisis and the Dreyfus affair.

In his later years, Forain created numerous scenes of the Law Courts and other Parisian institutions plus social satire caricatures of late 19th and early 20th century French life.