Background
He was the oldest son of John Cairnes of Donoghmore, company Donegal, and his wife Jane Miller, daughter of James Miller, Doctor of Medicine.
He was the oldest son of John Cairnes of Donoghmore, company Donegal, and his wife Jane Miller, daughter of James Miller, Doctor of Medicine.
Cairnes served in the British Army and took part in the Battle of Blenheim. In 1710, Cairnes entered the Irish House of Commons for Monaghan Borough, representing it until 1713. Subsequently he was returned for Monaghan County until 1727, when he stood also for Monaghan Borough.
Cairnes was appointed Keeper of Phoenix Park in 1712.
Thomas Sheridan thought him "an eminent Banker", but Jonathan Swift dismissed him as "a scrupulous puppy" and "a shuffling scoundrel". Mary Cairnes (died 28 August 1790) married Baron Blayney, and at the time of Cairnes"s death she was a childless widow.
One of the daughters, Elizabeth, married Robert Cuninghame, 1st Baron Rossmore, and another, Harriet, was the mother of Warner Westenra, 2nd Baron Rossmore, who succeeded to his maternal aunt"s husband"s barony by special remainder.
He was elected for both constituencies, however chose the latter and sat for it as Member of Parliament until his death in 1733. She subsequently remarried, in 1734, to Colonel John Murray, who was Member of Parliament for Monaghan County in the early 1740s.