Born in St Ives, Bill Marshall began assisting in the Leach Pottery at the age of fourteen, becoming its first full-time apprentice. He stayed for thirty-nine years (apart for the years during WWII), became Foreman in 1947, and continuing working until 1977. Initially he trained and then worked with David LEACH, until David left to set up his own pottery in Devon. Bill then worked (as Foreman) alongside Bernard LEACH, and helping teach many of the students who passed through the Pottery.  Whybrow especially notes the influence of the work of Shoji HAMADA upon Marshall, in terms of 'skill, values and working ethic.' 

Marshall's own skills were displayed particularly in the expressive art of throwing, and as Bernard grew older, Bill would throw pots to his design, leaving only the neck and the decoration to be finished by Leach; he became quite literally 'the hands of Leach'.  William left in 1977 to set up his own pottery in Lelant, where he was joined by his son Andrew MARSHALL.

His work was very highly regarded and much sought-after, in sales of work and exhibitions.