His daughter, Henrietta Elizabeth Williams-Wynn, married Thomas Cholmondeley, 1st Baron Delamere of Vale Royal (b. 9 Aug 1767, d. 30 Oct 1855). Sir Watkin made a Grand Tour to Europe from June 1768, returning by February the next year for his wedding in April. In Rome Pompeo Batoni painted him with some companions, and a classical subject, "Bacchus and Ariadne" was commissioned later, in 1774. The Rococo silver-gilt toilet service he gave to his first wife, by the London goldsmith Thomas Heming, is now in the National Museum of Wales. The Neoclassical grave monument for her is by Joseph Nollekens, in St Mary's Church, Ruabon, Clwyd. Sir Watkin played a significant role in the development of art in Wales, as an early patron of landscape painting there, which was to become the largest area of artistic activity in Wales. He brought both Richard Wilson and Paul Sandby to his seat at Wynnstay, Sandby staying six weeks in the summer of 1770, giving lessons to the family as well as painting, on his first visit to Wales. The next year Sandby returned and from 21 August to 4 September 1771 he and Sir Watkin toured through the mountains of northern Wales. From the sketches made on the tour Sandby published twelve aquatint "Views in North Wales" in 1776, and five of his "Views in Wales" of 1777. Matching sets from South Wales came from his tours there with Sir Joseph Banks, who commissioned the whole series. A more ambitious tour together, to Italy, was planned but cancelled after Sir Watkin's second marriage. 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. He supported the Concerts of Antient Music, and is caricatured by James Gilray in a depiction of King George III of England attending one he organized.