Sir William Fenwick, 2nd Baronet (c. 1617-9 July 1676), was an English baronet and MP.
He was the eldest surviving son of Sir John Fenwick, 1st Baronet of Wallington Hall, Northumberland and was educated at Morpeth Grammar School and Christ's College, Cambridge, before entering Grays Inn. He succeeded his father circa 1658, his half-brother John having been killed at Marston Moor in 1644.
He sat as Member of Parliament for Northumberland between 1645 and 1648, and in 1654, 1656, 1659, 1660 and 1661 to 1676.
He married Jane, the daughter of Henry Stapilton of Wighill, Yorkshire; they had a son and two daughters. He was succeeded by his son Sir John Fenwick, 3rd Baronet