Born in Bradford, Ontario, the 6 ft 3 in (1.91 m), 175 lb (79 kg) (12.5 stone) left-hander was signed by the Detroit Tigers as an amateur free agent before the 1964 season.

Kilkenny is perhaps best known for giving up Frank Robinson's 499th home run on September 13, 1971,[2] and also for being one of the few players in MLB history to play for four teams in the same season.

During his career, Kilkenny gave up 224 walks in just 410 innings, for a BB/9IP of 4.92, much higher than the American League average at that time.

On August 12, 1969, Kilkenny pitched a three-hit shutout against the California Angels for his first major league victory.

He was voted MVP during the regular season, winning the John Bell Memorial trophy with a 9–0 record and 129 strikeouts.