He was born into an Ulster Scots gentry family in 1686, the second son of Major John Montgomery and his first wife Catherine, the daughter of the Reverend James Auchinleck.
for County Monaghan and the grandfather of the famous American Revolution war-hero, Major-General Richard Montgomery).
[1] Up to 1729, Alexander Montgomery shared the parliamentary patronage of Lifford, County Donegal, with the Creighton family, later the Earls of Erne.
in Belfast) dated 1727 between Alexander Montgomery and General David Creighton about the sharing of Lifford Corporation and its representation in the Irish House of Commons, to which it sent two MP's.
On the death of the said Thomas Montgomery in 1761, full control of the Lifford seats passed to said Abraham Creighton.