After leaving his native Louisiana, Walston began his acting career in regional theater before landing a role in the legendary Maurice Evans production of "Hamlet" on Broadway in 1945. He worked steadily in New York theater throughout the late 1940s and early 50s, frequently collaborating with celebrated theater producer and director George Abbott. Walston reached his theatrical peak in the musical "Damn Yankees" (1955) playing Applegate, the devil/narrator, a performance which not only made him the toast of Broadway but garnered him a Tony Award for Best Actor in a Musical too.
After guest appearances on anthology TV series "Suspense" and "Playhouse 90" in the 50s, he debuted as a regular on the hit CBS comedy "My Favorite Martian", playing a space alien befriended by Los Angeles reporter Tim O'Hara (Bill Bixby) who eventually passed him off as his Uncle Martin. The series made Walston an American household icon during its three season run, and continued doing well in reruns.
Walston made his film debut in the forgettable "Kiss Them For Me" (1957), supporting Cary Grant and Jayne Mansfield. He recreated two stage roles in the film versions of the musicals "South Pacific" (1958) and "Damn Yankees" (1958). He was one of the philandering executives in Billy Wilder's "The Apartment" (1960), got most of the laughs in Joshua Logan's "Tall Story" (1960), starred as a nervous husband in Wilder's cynical domestic comedy "Kiss Me, Stupid" (1964), and played a grifter in George Roy Hill's "The Sting" (1973). Walston appeared in three Robert Altman directed films, as Poopdeck Pappy in the commercial disaster "Popeye" (1980), as the grandfather whose canceled insurance sparks the action in "O.C. & Stiggs" (1987), and as himself in "The Player" (1992).
Last seen on episodic TV in "Fast Times" (CBS, 1985-86), reprising his role on this small screen spin off of "Fast Times At Ridgemont High" (1982), Walston's TV career enjoyed something of a revival in the acclaimed drama "Picket Fences" (CBS, 1992-96) where he once again returned to series TV, this time playing a crusty old judge with the proverbial "heart of gold". For his efforts, he received two Emmy awards for supporting actor in a drama series.