Gasnier's earliest-known credits begin through his association with Max Linder, whom he is said to have discovered. Gasnier helmed many of Linder's earliest films and continued to work – sometimes as co-director with Linder – on projects featuring the comic through 1913. Gasnier also directed some films in Italy for Film d'Arte Italiana, a division of Pathé, with some featuring the legendary Italian film diva Francesca Bertini. Sadoul, writing in 1965, commented that Gasnier directed "100 to 200 films from 1909-1914" alone. No established filmography for Gasnier comes even close to such a figure in the stated period, suggesting that there are many French, and perhaps some Italian, films made by him which remain unidentified.