Mack Sennett's parents were working-class Irish immigrants who moved to Connecticut when he was 17. At first he hoped for a career as an opera singer, but he was working as a labourer when a 1902 meeting with Marie Dressler (also Canadian-born) elicited a letter of introduction to theatrical producer David Belasco. That too led nowhere, but Sennett stayed in New York to work as an actor, and in 1908 began appearing in films for the Biograph Studios, many of these films directed by D.W. Griffith, and eventually graduated to directing himself.
In 1912 he cofounded the Keystone film company, and in the next few years created there a style of wild and rambunctious comedy that made his name a byword for delirious, uninhibited slapstick. The stars of his company included such talents as Mabel Normand,"Fatty" Arbuckle, Chester Conklin, and, for a year, Charlie Chaplin, who made his first screen appearance for Sennett. The lunatic chorus of "Keystone Kops" was another feature of these films, many of which Sennett edited himself with consummate comic skill.
After 1917 Mack Sennett formed his own company and continued to produce comedies until the end of the silent era, but his career gradually declined in the 1930s until he was driven into a 4-year retirement to Canada in near penury in 1935. He returned to Hollywood in 1939 for a series of peripheral appointments, perhaps prompted by a special Academy Award presented to him in 1937. He was awarded a star on Canada's Walk of Fame in 2004.