A man of many musical capacities, Johnston was raised in Beverly Hills, where he was a member of a band named The Sleepwalkers. He also participated in one song with The Teddy Bears, he was a member of the Ritchie Valens band, and founder of the Surf Stompers as well as leader of The Rip Cords. He played various instruments in each of those bands, including the bass, guitar, keyboard and drums.
Johnston is frequently credited as one of the original greatest supporters of the Beach Boys' 1966 signature album Pet Sounds. He also helped, as a songwriter, to create some Barry Manilow hits and he released his own solo album, Going Public, in 1977.
Johnston is still currently touring with the Beach Boys.