Tierney was a right-handed batsman who bowled right-arm fast-medium. Tierney made his debut for Devon in the 1985 Minor Counties Championship against Cornwall. From 1985 to 1997, he represented the county in 35 Championship matches, the last of which came against Cheshire.
He made his MCCA Knockout Trophy debut for the county in 1985 against Wiltshire.
From 1985 to 1997, he represented the county in 22 Trophy matches, the last of which came against Shropshire. He played List A cricket for Devon at a time when they were permitted to take part in the domestic one-day competition, making his debut in that format in the 1985 National Westminster Trophy against Warwickshire.
From 1985 to 1991, he represented Devon in 5 List A matches, the last of which came in the 1991 National Westminster Trophy against Essex. In his 5 List A matches, he scored 43 runs at a batting average of 8.60, with a high score of 26.
With the ball he took 5 wickets at a bowling average of 50.40, with best figures of 3/47 against Warwickshire in 1985.