Classically trained on oboe, St John's first band was Ravishing Beauties with Virginia Astley and Nicky Holland.
The trio joined The Teardrop Explodes in Liverpool during the winter of 1981 for a series of dates at small clubs and a UK tour in early 1982.
In 1985 they had a worldwide hit with "Life in a Northern Town" and produced three albums: The Dream Academy (1985), Remembrance Days (1987) and A Different Kind of Weather (1990).
This led to the formation of Channel Light Vessel, a band with Kate, Roger Eno, Bill Nelson, Laraaji and Mayumi Tachibana.
St John and her husband and writing partner, Neill MacColl, specialise in on set music production in films, having worked on Far From The Madding Crowd (2015), Tulip Fever (2017), My Cousin Rachel (2017), and The Little Stranger (2018).