He played for Manly-Warringah the New South Wales Rugby League (NSWRL) competition, and Hull FC in England.
Willoughby was not selected to play for Manly in the 1972 NSWRL grand final where the club won its maiden premiership defeating Eastern Suburbs 19–14.
Willoughby played in Manly's 1975 preliminary final loss against Eastern Suburbs scoring a try in a 28–13 defeat.
In the second half and with 10 minutes remaining, Parramatta made a play to the right hand side of the field and the ball eventually reached Neville Glover.
In 1978, Willoughby missed the entire season through injury as Manly won their 4th premiership defeating Cronulla in the grand final.