A former first-round pick of the San Francisco Giants, Fenwick was taken by the Astros in the Rule 5 draft and played in 36 games in 1972, batting .180 with four runs batted in.

He was traded the next off-season to St. Louis in the Skip Jutze deal but was released by the Cardinals and signed, again, with the Astros in 1973 but did not play in the majors for them.