Background
He was the third and youngest son of John Cairnes and his wife Jane Miller, daughter of James Miller.
He was the third and youngest son of John Cairnes and his wife Jane Miller, daughter of James Miller.
Another brother was William Cairnes. In 1732, Cairnes entered the Irish House of Commons for Monaghan Borough, the same constituency Alexander had represented before, and sat for it until his death in 1743. He died childless on 16 June 1743 and with his death the baronetcy became extinct.
His will was proven on 24 August 1745.
His widow died on 8 March 1750 and was buried 3 days later at Putney.