Sir Watkin Williams-Wynn, 3rd Baronet (1692 – 26 September 1749) was a Welsh politician and prominent Jacobite.
Sir Watkin was the eldest son and heir of Sir William Williams, 2nd Baronet, of Llanforda near Oswestry; his mother, Jane Thelwall, was a descendant of the antiquary, Sir John Wynn of Gwydir, Caernarfonshire. The name "Watkin Williams-Wynn" was common to several of the later baronets. There is a Welsh folk song named after the best-known of these.
Educated at Jesus College, Oxford, Williams-Wynn succeeded to the baronetcy and his father's estates on the death of his father in 1740 and also inherited Wynnstay near Ruabon and the other estates of the Wynn baronets of Gwydir which had been left to his mother on the death of Sir John Wynn in 1719. A lifelong Tory, he was Member of Parliament for Denbighshire from 1716 until his death, but for a brief interlude from 1741–1742, and was prominent among the opponents of Sir Robert Walpole. He was also elected for the borough of Beaumaris in 1727 but chose to sit for Denbighshire.
In the election of 1741, the Walpole administration targeted his Denbighshire seat. Although Wynn won the popular vote by 1352 votes to 933 the sheriff disallowed 594 of Wynn's votes and returned his rival. Walpole's first defeat in the ensuing parliament was in a dispute of this election, and after Walpole's resignation early in 1742 Wynn won the seat back and the sheriff was jailed. In the meantime Williams-Wynn sat for Montgomeryshire, vacating the seat on his re-election to Denbighshire.