He was the eldest son of Dr. Alexander Monro (primus) of the distinguished Munro of Auchinbowie family.
John received his early education at Mr Mundell's school in Edinburgh and was admitted an advocate on 24 July 1753 at the age of twenty-seven.
He had a fair practice and on 21 January 1758 he was appointed Procurator Fiscal or Crown Prosecutor in the High Court of Admiralty on the nomination of the Judge, his brother-in-law James Philp.
On 8 July 1757 Monro married Sophia, daughter of the deceased Archibald Inglis of Auchindinny, Midlothian and Langbyres, Lanakshire, the eldest of three co-heiresses.
Monro died on Sunday 24 May 1789 aged sixty-three and as he made no will, Auchinbowie was divided between two daughters.