In March 1746 he was appointed Secretary in succession to John Murray of Broughton.
His competence was criticised by Lord George Murray, who blamed him for logistical failures while Quartermaster before the Battle of Culloden.
[1] He followed Prince Charles into exile and continued to serve in his personal retinue.
Hay accompanied Charles to Rome following the death of James Francis Edward Stuart in January 1766 and was appointed Major-Domo of the Household in place of Sir John Constable.
Through his marriage to Anne, the only child of James Elphinstone, he became the owner of Restalrig House in Edinburgh.