Foster has been a member of the Royal Society of Portrait Painters since 1976 and President since 2017. Furthermore, he served as Vice-President from 1991 to 1994 and Treasurer from 2003 to 2006. Foster has also acted as a member of the Art Workers Guild since 1980.
Over his career, he has tried to be as diverse as possible and has painted a great variety of pictures in both oil and watercolour, not just single portraits and groups, but also landscapes and compositions which he exhibits at his one-man shows every three or four years .