His first professional post was as harpist with the Bournemouth Symphony Orchestra, later joining the Orchestra Of The Royal Opera House, Covent Garden. During the 1960's, 70's and 80's he also played for various London session orchestras, and in this way he contributed to many film and television scores and chart successes. He also played in the groups of several jazz musicians such as John Dankworth.
Another area Snell was particularly active in was library music, composing many incidental scores for use in television, radio and film productions during the 1970s and 80s, for companies including KPM Music, Bruton Music, Parry Music Ltd and Josef Weinberger Limited. While working for the music libraries he also played on the recordings of many of the era's musical directors and arrangers such as Alan Hawkshaw, Keith Mansfield and John Cameron.