Mackay played his junior rugby league for Alexandria Rovers in the South Sydney competition but signed with rivals Eastern Suburbs in 1973.He also played for Paddington Colts in the Eastern Suburbs Junior League from 1969 to 1972.
Mackay was selected to play at prop in Easts 19-4 victory over Canterbury-Bankstown in the 1974 NSWRL grand final at the Sydney Cricket Ground winning their first premiership in 29 years.
At club level, Eastern Suburbs went on to claim the 1975 minor premiership and reach the 1975 NSWRL grand final against St George.
Easts went on to win their second straight premiership defeating St George 38-0 at the Sydney Cricket Ground with Mackay scoring a try.
The match is mainly remembered for the white boots worn by St George player Graeme Langlands.