As a boy in Glasgow, Campbell had a distinct unique style of guitar playing, whereby he played left-handed, with the strings upside down, right hand strung - tuned to "open E".
He joined Pat Fairley to form "Dean Ford and the Gaylords" later to become "The Marmalade", on his fourteenth birthday in May 1961. With "The Marmalade" he co-wrote and produced the multi-million selling hits "Reflections of My Life", "Rainbow" and "I See the Rain", amongst others, in a long line of world chart hits from 1967 to 1971. Campbell's guitar solos on "Reflections of My Life" and "I See the Rain" are particularly outstanding; the latter was named Jimi Hendrix's favourite cut of 1967.
Tired of touring, Campbell left "The Marmalade" in March, 1971.
During the 1970s, Campbell released two solo records, "Hallelujah Freedom", and "Sweet Illusion", both of which made top-10 chart appearances in the UK Singles Chart. He studied orchestration and composition with Eric Guilder and Max Saunders at the RCM, and became an arranger and producer for many artists, including Barbara Dickson.
Campbell has composed music for television and film, including the 1994 BAFTA-winner "Taking Over the Asylum", starring David Tennant and Ken Stott, and the 1998 adaptation of the highly acclaimed BBC Worldwide Minette Walters murder mystery "The Scolds Bridle".
At some point Mike O'Donnell and Junior Campbell signed to the same publisher, and their partnership sparked. They have collaborated on writing television jingles, which continued even after leaving their bands.
The two have composed many "Thomas" theme songs like "Thomas Anthem", "Really Useful Engine", "It's Great to be an Engine", "Accidents will Happen", "Every Cloud has a Silver Lining" and "Down by the Docks".
Campbell currently lives in Sussex with his wife Susie, and has three children and three grandchildren.
It is likely that he and Mike O'Donnell based the TUGS opening and ending themes on his song, "Do You Have To Fall In Love."