Noble and politician. The eldest son of George Hay, the 8th Earl, who he succeeded in 1758, Hay served as a Member of Parliament for Cambridge (England) between 1741 and 1758, although his seat was at Dupplin Castle, southwest of Perth. He went on to become Chancellor of the Duchy of Lancaster (1758-62). He also served as Chancellor of the University of St Andrews (1765-87).
He married in London, but his only son died in infancy.
Hay died in Dupplin Castle and lies buried in a family vault in Aberdalgie Kirk, a church he was responsible for rebuilding in 1773.