In his time at Ponty, Johnston was selected for Wales U21s and Wales 7s and was involved in the squad that won the Welsh Cup in 2002 and narrowly lost to Sale in the Parker Pen European Shield Final. After regional rugby was formed he returned to Neath RFC winning the league twice and Welsh Cup in a three-year stint.
During Johnston's time at Ponty, he was selected for Wales U21s and Wales 7s and played with the squad that won the Welsh Cup in 2002 and narrowly lost to Sale in the Parker Pen European Shield Final. After regional rugby was formed, he returned to Neath RFC where he won the league twice and the Welsh Cup over a three-year period.