Sir William Brownlow, 4th Baronet (5 November 1665 – 6 March 1701) was an English Member of Parliament.
Brownlow was the younger son of Sir Richard Brownlow, 2nd Baronet, and Elizabeth Freke and was educated at Sidney Sussex College, Cambridge.
He was elected to the House of Commons for Peterborough in 1689, a seat he held until 1698, and then represented Bishop's Castle from 1698 to 1700. In 1697 he succeeded his elder brother as fourth Baronet of Humby.
Brownlow married firstly Dorothy, daughter of Sir Richard Mason and granddaughter of Sir James Long, 2nd Baronet. Dorothy died in 1700, and he married secondly a few months later, Henrietta Brett, the sister of Colonel Henry Brett. (Col. Brett married Dorothy's sister Anna, the notorious divorced Countess of Macclesfield). Brownlow died in March 1701, aged only 35, and was succeeded by his son from his first marriage John Brownlow, who in 1718 was raised to the peerage as Viscount Tyrconnel.