William learnt to swim at the age of 18 months, and was freediving to 15m by the age of 8, however he did not begin serious training for the sport until 2003. In 2004 he became the first non-Italian instructor at Umberto Pelizzari's prestigious Apnea Academy. Since then he has trained extensively with Pelizzari, and written the translations of 'Manual of Freediving' (Idelson & Gnocchi) and the Apnea Academy Instructors Manual.

William holds the world record in the discipline of Unassisted Constant Weight (no fins), and can dive to over 86 meters (282 feet) without the use of fins, rope, weight, or any other form of assistance. He also holds the world record in the discipline Free Immersion, at 108m (354 feet). He currently trains in Italy in the summers and Dean's Blue Hole in the winter.