As his grandparents came from County Donegal, he visited Ireland many times, throughout his childhood, and still has a home there.
In 1969 he formed the Scottish folk group Contraband, who released an album in 1974, then disbanded in 1975.
He became one of the first to compose using both traditional and classical musicians, and his "Wellpark Suite" in 1985 was generally acclaimed as a milestone in Scottish music.
From 1989 William Jackson released a series of albums on his own label Mill Records, sometimes using ancient texts, and on one occasion a poem by Kahlil Gibran.
He arranged and performed the music for Battle of the Clans, a documentary on The History Channel.