A cinema pioneer, Gasnier shepherded the early career of comedian Max Linder, co-directed the enormously successful film serial The Perils of Pauline (1914).

Gasnier capped his output with the notorious low-budget exploitation film Reefer Madness (1936) which though both a critical and box office failure, became a cult classic.

With the public, Gasnier was associated with high adventure in exotic locales, such as what was endemic to serials, or with social melodrama of the kind that was popular in the early 1920s.

Gasnier went into the dawn of talking pictures as a Paramount director, though mainly working on their foreign-language productions; his command of the English language – even after living many years in the United States – was at best limited.

Grand National swiftly flopped, and was liquidated in 1939; its studios were taken over by Producers Releasing Corporation; Gasnier did not elect to stay with PRC, but he did remain with Hirliman, finishing out his directorial career with a couple of features at Monogram Pictures and then retiring upon reaching the age of 65.

Re-released theatrically in 1972, it swiftly attracted a devoted cult following among "midnight movie" fans in the 1970s and 1980s through its showings in repertory cinemas and by college film societies.

Max Linder compromised forever his considerable comic legacy through his tragic and incomprehensible death in a double suicide (or suicide-homicide) involving himself, and his young wife in 1925.

Gasnier's poor English was once blamed for the barely literate subtitles in The Perils of Pauline, but this was debunked in the 1960s by Arthur Charles Miller and William K. Everson.

Although the content of Reefer Madness is generally considered so ludicrous as to be harmless, it has been criticized extensively for its complicity in the passage of the Marihuana Tax Act of 1937, which criminalized marijuana.

Gasnier's directorial style was not heavily involved in rich visual content or dynamic editing; he was principally interested in basic storytelling and liked to work in a producer-like, supervisory role.

One reason Reefer Madness is so well known in comparison to Dwain Esper's wild, but amateurish Marihuana or Elmer Clifton's dull, soap operatic Assassin of Youth is that it is a much better-made film than either of those.

Despite being dubbed "consistently mediocre" by the All Movie Guide's Hal Erickson, it remains difficult to evaluate Gasnier's relative strengths and weaknesses as a director based on what survives of his work from the silent period.

Gasnier's version of Maytime (1923)—the first screen adaptation of the Romberg operetta, later remade by Robert Z. Leonard into a vehicle for Nelson Eddy and Jeanette MacDonald—was found along with a cache of American films discovered in New Zealand in 2010.