Kerrigan worked as a newspaper reporter until 1907 when he joined the famous Abbey Players. There he became a stalwart, appearing in plays by Lady Gregory, John Millington Synge, William Butler Yeats, and Sean O'Casey (for whom he played the role of Jimmy Farrell in The Playboy of the Western World.
He settled permanently in Hollywood in 1935, having been recruited along with several other Abbey performers, to appear in John Ford's The Informer. In that film and in Ford's The Long Voyage Home, he plays similar roles, that of a leech who attaches himself to men until they run out of money. Perhaps his best known role was in The General Died at Dawn, where he plays a character actually named Leach, in which he steals scenes from Gary Cooper, Madeleine Carroll, and William Frawley. In it he plays a sinister little petty thief who, holding a gun on Cooper, says, "I may be fat, but I'm agile." Regrettably, in the forties and fifties he rarely got good parts and eventually became little more that a bit player.
He had very little screen time in films which he starred as minor roles, such as the "First Drayman" in Merely Mary Ann (1931) with Janet Gaynor. One of his most recognizable minor roles in Gone with the Wind (1939), when he played John Gallegher, the seemly jovial mill owner who whips his convict labour in to "co-operation". He also appeared in Walt Disney's 1954 famous film version of Jules Verne's Twenty Thousand Leagues Under the Sea in a minor role at the beginning of the film.
Despite having small roles, Kerrigan has a "Star" on the Hollywood Walk of Fame at 6621 Hollywood Blvd.