His father Willam Forbes, heir to a Nova Scotia baronetcy, was an advocate; the family estate at Monymusk in Aberdeenshire had been sold by his grandfather.
The younger boy died in 1749, and in October 1753 Lady Forbes, with her surviving son, settled in Edinburgh.
[2] A friend of the family, Sir Francis Farquharson of Haughton, arranged with Messrs. Coutts, a prominent firm of bankers in Edinburgh, to admit Forbes as an apprentice, and he entered their service in 1754.
[2] From 1763 to 1773 the active members of the firm, still under the original name, were Sir Robert Herries, Forbes, and James Hunter.
The name Coutts was retained till 1773, when a new contract was made, and the firm became Forbes, Hunter, & Co., Sir William Herries having settled in London to conduct in St James's Street the business later known as Herries & Co. Forbes was now the head of the firm, and decided to confine the transactions of the house to banking alone.
The property passed to the son William on his death, and is now the main building of Merchiston Castle School.
He was a member of Samuel Johnson's literary dining club, and he is mentioned in James Boswell's Tour to the Hebrides.
[2] He is buried in Greyfriars Kirkyard in the vault immediately east of MacKenzie's domed tomb on the south side.
The vault was built at the height of the graverobbing fears in Edinburgh and demonstrates the design art of "secure burial".
Miss Hay was a noted singer with the Edinburgh Music Society based in St Cecilia's Hall.