In the 1960s, Walker appeared in a 1962 episode ("Across Walnuts and Wine", S3E07) of the classic television series Route 66. He played the title role and an emotionally disturbed character who was a troubled actor who lived and performed on the streets and in circuses, in Naked City episode "Dust Devil on a Quiet Street" from November 28, 1962. In The Big Valley episode "My Son, My Son," aired on November 3, 1965 (S1E08), Walker portrayed Evan Miles, an emotionally disturbed college dropout who becomes obsessed with childhood friend Audra Barkley. He had a memorable role in Star Trek as Charles 'Charlie' Evans, a 17-year-old adolescent and social misfit with psychic powers in the episode "Charlie X", which aired September 15, 1966 (S1E02). Walker appeared in the fifth season of the series Combat! in the episode "Ollie Joe" on September 27, 1966 (S5E03). In addition he had the title role in "Billy the Kid," episode 22 of The Time Tunnel, which originally aired on February 10, 1967. He also portrayed Nick Baxter, an ill alien who caused the deaths of humans by touch, in the episode "Panic" in the television series The Invaders, which aired on April 11, 1967 (S1E14). He played Mark Cole in the October 29, 1967, episode of Bonanza titled "The Gentle Ones" (S09E07).