In 1982 he captained Scotland to victory in the UEFA European Under-18 Championship, the only major trophy won by any Scottish national football team. He captained each of the Scotland teams from under-16 level through under-18, under-20, under-21 and senior level. McStay made his full national team debut in 1983. He represented Scotland 76 times, including appearances at two World Cups in 1986 and 1990, during a 14-year international career. McStay was also selected for two UEFA European Championships in 1992 and 1996, but withdrew from the latter because of an ankle injury.