Fenwick played rugby as a schoolboy for Caerphilly Grammar Technical School, and later joined Taffs Well RFC.
In 1971 he switched to Beddau where he played 51 games before moving on to the first class team Bridgend.
While at Bridgend Fenwick earned all of his 30 international caps for Wales, making his début against France in 1975, in which he scored a try after only five minutes, and finished the game with a personal tally of 9 points.
[1] On this tour he played 9 provincial games and 4 tests and scored 2 Tries, 1 con and 3 pens.
Fenwick went on to win two caps with the Wales national rugby league team between 1981 and 1982 scoring five goals.