Early life
McLaglen was born in Tunbridge Wells, Kent. His father, later a bishop of the Free Protestant Episcopal Church of England, moved the family to South Africa when McLaglen was a child. He had eight brothers and a sister. Four of his brothers also became actors: Arthur (1888–1972), an actor and sculptor, and Clifford (1892–1978), Cyril (1899–1987) and Kenneth (circa 1901-1979). Other siblings included Frederick (b. circa 1882), Sydney (b. circa 1884), Lewis (b. circa 1889), and a sister, Lily (b. circa 1893). Another brother, Leopold McLaglen, who appeared in one film, gained notoriety prior to World War I as a showman and self-proclaimed World Jujutsu Champion, who authored a book on the subject.

Film Career
McLaglen's career took a surprise turn in the 1920s, when he moved to Hollywood. He became a popular character actor, with a particular knack for playing drunks. He also usually played Irishmen, leading many film fans to mistakenly assume he was Irish rather than English. McLaglen played one of the titular Unholy Three in Lon Chaney, Sr.'s original silent version of the macabre crime drama. The highlight of his career was an Academy Award for Best Actor for his role in The Informer (1935), based on a novel by Liam O'Flaherty; Frank Tashlin's 1938 cartoon Have You Got Any Castles? features a caricature of McLaglen emerging from the novel and literally informing someone about some shady characters. Arguably his most famous film remains Gunga Din (1939) with Cary Grant and Douglas Fairbanks, Jr., an adventure epic loosely based on Rudyard Kipling's poem and partially remade decades later as Indiana Jones and the Temple of Doom (1984). McLaglen was nominated again, this time for Best Supporting Actor for his role opposite John Wayne in The Quiet Man (1952). He was especially popular with director John Ford, who frequently included McLaglen in his films, often as comedy relief. Toward the end of his career, McLaglen made several guest appearances on television, particularly in Western series such as Have Gun, Will Travel and Rawhide. The episodes of those series in which McLaglen guest-starred were both directed by his son, Andrew V. McLaglen, who later was a film director frequently directing John Wayne.