Apprenticed in 1742 to Archibald Wallace and James Stewart, a firm of Edinburgh merchants,
After his brief parliamentary experience Hay apparently became ambitious of establishing himself as a landed proprietor. His brother, Dr. James Hay, had succeeded in 1762 to the estate of Haystoun. Adam now proceeded to acquire the nearby lands of Soonhope, formerly the property of his family, and built a mansion near Peebles called Hay’s Lodge.
In May 1775 James Montgomery vacated his seat, and on 17 June Hay was unanimously elected in his place. He may have hoped, as an M.P., to escape his creditors until the end of the Parliament.
It is not known whether he took his seat in the new session beginning 26 Oct. On 15 Nov. 1775 he died in London. George Selwyn wrote to Lord Carlisle, 16 Nov. 1775:
Adam Hay, Lord March’s Member for Peebles, died yesterday, I am afraid to say suddenly because it is a suspicious word, and will be more so in his case, as I believe fortune has not been favourable to him. But I do not believe anything of that sort; his general state of health has been bad for some time and I was told that his last and fatal attack was in his bowels.
Hay’s affairs were in such confusion that his property had to be sold to pay his debts, and his estate of Soonhope was bought by his brother, Dr. James Hay of Haystoun, in 1778.
