Chapman first joined UFO in 1974 as a second guitarist to augment their live sound having answered an advert in UK's music paper, Melody Maker.

He left UFO in January 1975 due to personal differences with the band,[4] and went on to form Lone Star, where he remained until June 1978.

In 1977, he filled in for Michael Schenker in UFO when they were on tour with Rush in the United States during one of the German guitarist's absences.

After resuming with Lone Star following the tour, Chapman later rejoined UFO in December 1978 on a full-time basis after Schenker parted company with the band.

After the tour, Chapman went to Florida, United States, to form a new band DOA fronted by lead singers Ray Williams, Dave Edwards, Bass player Steve Chikitus, guitarists Jon Smyth, Robert Journey and Drummer Paul Baron.

Paul's Florida band DOA was later renamed Madman who toured with Ted Nugent in the United States.

A solo instrumental track, "The Bells of Berlin" appeared as part of the December 2000 archive Waysted collection Your Prayers Are Saved.

He enlisted the help of Robin McAuley who sang on versions of "No Place To Run", "Wild, Willing & Innocent" and "The Writer" cut at Garudio Studios in Palm Bay.

In July 2006, Chapman joined the American southern rock band Gator Country, a collection of Molly Hatchet veterans.