William Letheren played for Exeter City in the Plymouth and District League before the club turned professional in 1908.

Joining from the disbanded Exeter Argyle along with Henry Dyer and William Stoneman, he played in the public practice match on 30 August 1907 ahead of making his competitive debut against Torpoint on 21 September 1907.

Making 22 appearances during Exeter City’s final amateur season he did not, in common with nearly all of his teammates, become a professional although he stayed with the club as an amateur and played for the reserves until 1911/12.