Born in Richmond, Quebec, Mack Sennett's parents were Irish immigrants. When he was 17, the family moved to East Berlin, Connecticut and later, Northampton, Massachusetts, where Mack worked as a labourer. After a chance meeting with actress Marie Dressler in 1902, Sennett went to New York to try for a career on the stage. He earned chorus boy parts, and eventually began acting in films in 1908, appearing alongside a number of Hollywood stars, including fellow Canadian Mary Pickford.
By 1910 he was directing, and in 1912 he co-founded the Keystone production company. Sennett "discovered" many future stars, including Gloria Swanson, Harry Langdon and Charlie Chaplin, who Sennet directed in 35 comedies during 1914 alone. Sennett's trademark films leaned heavily towards one-reel comedies with wild slapstick chases, ususally ending with policemen falling over themselves - the classic "Keystone Kops".
Sennett directed and produced hundreds of films, and despite some ups and downs later on in his career, was awarded a special Oscar in 1937 - "to the master of fun, discoverer of stars ... for his lasting contribution to the comedy technique of the screen".