In the 1990s, St John was a member of Van Morrison's live band playing oboe and saxophone. She played on five Van Morrison albums. In 1994, she co-wrote and sang on four tracks with Roger Eno on the album The Familiar on the All Saints Label. This led to the formation of Channel Light Vessel, a band with Kate, Roger Eno, Bill Nelson, Laraaji and Mayumi Tachibana.
St John has released two solo albums: Indescribable Night (1995) and Second Sight (1997).