Sir Watkin commissioned Robert Adam to build 20–21 St James's Square in London which was constructed between 1771 and 1775. Sir Joshua Reynolds received several commissions from Sir Watkin, some of which remain with the family. These include a portrait of him with his first wife in "Van Dyck" costume, and another of his second wife with her children, in around 1784, one with his mother (1768–69, National Gallery, London), one of Sir Watkin presiding over the Society of Dilettanti (1777, now on loan to Brooks' Club), and one of his eldest son as John the Baptist.