[4] Furth wrote the plays Twigs, The Supporting Cast, and Precious Sons as well as the book for the Kander and Ebb musical The Act.

[citation needed] Frequently cast as a bespectacled, ineffectual milquetoast, Furth appeared in The Boston Strangler, Butch Cassidy and the Sundance Kid (as a devoted railroad employee travelling in the car that contains the safe that Butch and his gang twice rob), Myra Breckinridge, Blazing Saddles, Shampoo (as a bank officer dealing with Warren Beatty’s character’s loan request), Oh, God!

(as a newspaper editor who refuses to publicize John Denver’s character’s claims that God has communicated with him), The Cannonball Run, The Man with Two Brains, and Bulworth.

His many television credits include Mary Hartman, Mary Hartman; 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 TV movie The Scarlett O'Hara War, in which he portrayed George Cukor.

[5] He also worked as a voice actor in several episodes of the animated television series The Adventures of Don Coyote and Sancho Panda for Hanna-Barbera Productions.