Thursfield was born in Oxford in England, moving to Australia at age 3.[1]
Will attended Brighton Grammar and in years 8–10 and played in the 1st XVII. In 2003 he played in the combined APS team against AGS (Associated Grammar Schools).
Thursfield made his debut in round 14, 2005 against eventual premiers Sydney. His first assignment was handling key-forward Michael O'Loughlin. He impressed straight away by keeping the Swans forward to 1 goal, as the Tigers upset Sydney by a solitary point.
Thursfield retired at the end of the 2011 season, having played ten senior matches for the year. He stated that, although he was "proud to have played the game at the highest level over the past seven seasons", there were "some other avenues in [his] life" that he was "keen to pursue".[3]