 Thornett was a second-rower, and joined his brother Ken at the Parramatta Eels in 1963.He played there until 1971, making 168 appearances for the club, being a master ball player informing the style-changing ball skills that Arthur Beetson would bring to forward play shortly after Thornett.In a club game against Canterbury in 1968 Thornett matched the then standing club record of four tries in a match.