Mackay made his full All Whites debut in a 4-0 win over Mexico on 20 August 1980. He represented the All Whites for all three matches at the 1982 FIFA World Cup in Spain, where they lost to Scotland, USSR and Brazil. Mackay ended his international playing career having played 48 times for New Zealand, of which 36 were A-international caps. He scored a solitary goal in A-internationals. his final cap a substitute appearance in a 1-1 draw with Fiji on 18 October 1984.