The son of a wealthy merchant, Mason decided he could make more money on the stage than designing buildings, and played with the Old Vic and the Gate Company in Dublin. He first appeared onscreen in British "quota quickies" and caused a sensation as a handsome, sadistic aristocrat in the 1943 costume drama, "The Man in Grey".

After another triumphant appearance in Carol Reed's Irish suspense thriller, "Odd Man Out" (1947), the brooding, gifted Mason became Britain's biggest star, moving to Hollywood soon after. Although Southern California softened his rougher edges, he soon reaffirmed his niche as an urbane matinee idol with a dark side. This persona was exploited to international success in the Cukor-Garland remake of "A Star Is Born" (1954), with Mason playing complex, Barrymore-style monster Norman Maine (a role which Cary Grant had turned down).

Though gifted with a distinctive, beautiful speaking voice, and with a range much deeper than that of a conventional leading man, Mason nevertheless had trouble finding the kind of quality roles he deserved. His filmography is generally undistinguished, but contains several gems, including: "20,000 Leagues Under the Sea" (1954), as the obsessed Captain Nemo; Hitchcock's "North by Northwest" (1959), this time opposite Cary Grant; Kubrick's "Lolita" (1962), featuring his sterling, poignant work as Humbert Humbert; the Harold Pinter-scripted "The Pumpkin Eater" (1964); and "Georgy Girl" (1966), as the aging roue in pursuit of Lynn Redgrave. Mason received a Best Supporting Actor Oscar nomination for his role in 1982's "The Verdict". At one time married to actress (and later columnist and TV host) Pamela Mason, he was the father of actress-author Portland Mason and producer Morgan Mason.