[2] On his marriage, Coutts was taken into partnership by his wife's uncle, George Campbell, head of the Whig bank in the Strand who counted John Stuart, 3rd Earl of Bute as a customer.

The fair character you bore with everybody and your very becoming deportment in business and in every other situation of life made me feel the most sensible concern to see you appear so unlike yourself.

[2] In 1774, on the expiration of their 12 years partnership agreement, his brother Thomas took steps to protect the bank's credit from James' perceived "irresponsible actions.

"[2] Lord Bute, Stuart Mackenzie, Sir John Pringle and family friends signed a declaration that James was "an improper person to be connected with such a business" and he was forced to accept a financial settlement which he bitterly protested.

[2] In April 1755 Coutts was married to heiress Mary "Polly" Peagrum at St George's Hanover Square Church in London.

[2] Through his only child Frances, he was a grandfather of Sir John James Stuart, 5th Baronet of Allanbank, who married twice, but had no children by either marriage, therefore, the baronetcy ended with his death in 1849.