William Marshall's relationship with clay began in 1934, when David Leach visited St Ives School looking for apprentices for the Leach workshop.  Bill, a boy of 14, raised his hand becoming the Leach Pottery's first apprentice.  Progressing to Foreman, over the next forty two years, William Marshall was responsible for overseeing the standard ware, as well as the training of the young apprentices who passed through.

William Marshall later came to be regarded as Bernard Leach’s right hand man, assisting with the making of some of Bernard’s larger and more complex pots. By the 1950s he had developed his own work, distinct from Bernard Leach’s yet influenced by Japanese aesthetics; an imagined aesthetic as opposed to experienced one, as he never visited Japan.  He finally left the Leach Pottery in 1977, two years before Bernard Leach’s death, to set up his own pottery in Lelant establishing himself as a master potter in his own right.