Stardom finally came with a leading role in "His Hour" (1924), an adaptation of a heavy-breathing Elinor Glyn romance. Gilbert signed with MGM that year, the studio which would make him a major star in the mid-1920s and break him a few years later. He had good roles in "He Who Gets Slapped" (1924, starring Lon Chaney) and as a roguish villain in "The Snob" (also 1924) before starring with Mae Murray in Erich von Stroheim's highly successful but problem-plagued "The Merry Widow" (1925). He went on to prove himself both a handsome lead and a talented actor in two films directed by King Vidor: the WWI story "The Big Parade" (1925) and "La Boheme" (1926).
The romantic, headstrong Gilbert tended to fall in love with actresses, particularly his co-stars. He married and divorced Olivia Burwell, Leatrice Joy (with whom he had a daughter), Ina Claire and Virginia Bruce. But his most high-profile romance began in 1926 when he co-starred with recent import Greta Garbo in "Flesh and the Devil". The on-again, off-again affair lasted three years, and the two successfully co-starred in "Love" (a modern-dress "Anna Karenina", 1927) and "A Woman of Affairs" (1929). His other leading ladies included Joan Crawford ("Twelve Miles Out", 1927 and "Four Walls", 1928), Renee Adoree ("The Show", 1927 and "The Cossacks", 1928) and stage great Jeanne Eagels ("Man, Woman, and Sin", 1928).
Gilbert's career ended with a crash when talkies arrived, and it's generally assumed that his voice was to blame. Actually, he had a perfectly serviceable voice: it was a personality clash with Louis B Mayer and poor films that did him in. Dim, badly-written fare like "His Glorious Night" (1929), "Redemption" and "Way for a Sailor" (both 1930), "Gentleman's Fate" (1931) and "Fast Workers" (1933) may indeed have been a plot to end Gilbert's career. There were a few high points: he played a magician/thief in "The Phantom of Paris" (1931) and a charming, soulless servant in "Downstairs" (1932). Garbo kindly insisted he co-star with her in "Queen Christina" (1933), but it wasn't much of a role. By that time, he was drinking heavily and more quarrelsome than ever. Gilbert's last hurrah was as an alcoholic would-be writer in "The Captain Hates the Sea" (1935). He turned in a brilliant character performance, and current love Marlene Dietrich was trying to hire him for a second lead in "Desire" (1936) when he died of a heart attack.