Frequently cast as a bespectacled, ineffectual milquetoast, Furth appeared in such films as The Boston Strangler, Butch Cassidy and the Sundance Kid, Myra Breckinridge, Blazing Saddles, Shampoo, The Cannonball Run, The Man with Two Brains, and Bulworth. His many television credits include Tammy, McHale's Navy, Ironside, I Dream of Jeannie, That Girl, Green Acres, The Monkees, Batman, The Odd Couple, Bonanza, Happy Days, All in the Family, Murphy Brown, L.A. Law, Dr. Quinn, Medicine Woman, Murder, She Wrote, Little House on the Prairie, Love, American Style, Adam-12, F Troop and the 1980 made-for-TV film The Scarlett O'Hara War, in which he portrayed famed film Director George Cukor. He was a regular in the cast of the short-lived 1976 situation comedy The Dumplings.