Although Martian had somewhat typecast him and he had difficulty finding more serious roles after the show's cancellation, he managed to return to beloved character actor status in television of the 1970s and 1980s, appearing as a guest star in numerous shows, such as Wild Wild West, Love, American Style, The Rookies, Mission: Impossible, Ellery Queen, The Six Million Dollar Man, Little House on the Prairie, and The Incredible Hulk with Bill Bixby (in which he played Jasper the Magician in an episode called "My Favorite Magician"), among many others. In 1976 he played the part of Edgar Whiney in the film Silver Streak. From 1980 to 1992, Walston starred in fourteen movies. Perhaps most notable was his performance as Mr. Hand in 1982's Fast Times at Ridgemont High, as well as its 1986 television adaptation.

In 1984, Walston played a judge on an episode of Night Court. Six years later, he would work with David E. Kelley while guest-starring on L.A. Law as a suffering father. These roles led to his work as Judge Henry Bone on Picket Fences, which began production in 1992 for CBS. Judge Bone was originally a recurring role on the show, but Walston proved to be so popular that he was given a starring role the following year. In his late 70s, he was nominated for an Emmy Award for the first time. Walston made an appearance in Star Trek: The Next Generation as Boothby, head groundskeeper at Starfleet Academy in San Francisco, and then reprised the character twice on Star Trek: Voyager, despite the series being set in a distant part of the galaxy.

After gaining popularity both as the Martian and as the judge on the small screen, his career was coming to an end when he played Grandfather Walter Addams in Addams Family Reunion (1998), the straight-to-video second sequel to the blockbuster 1991 film The Addams Family, this time starring Tim Curry as Gomez Addams and Daryl Hannah as Morticia Addams. One year later, he appeared in the movie remake of his hit series, My Favorite Martian (1999). His final movie role was in the independent film AT&T long distance TV commercial in which his dialogue implied he was Uncle Martin from Mars, looking for good rates to talk to fellow Martians living in the United States. Just before his death, his final TV guest appearance was on 7th Heaven. Walston died on New Year's Day 2001 in Beverly Hills, California, just one month after his 86th birthday, after a 6-year battle with lupus.