William de Burgh, 3rd Earl of Ulster and 4th Baron of Connaught (English: /dəˈbɜːr/ də-BUR; 17 September 1312 – 6 June 1333) was an Irish noble who was Lieutenant of Ireland (1331) and whose murder, aged 20, led to the Burke Civil War.

He was summoned to Parliament from 10 December 1327 to 15 June 1328 by writs addressed to Willelmo de Burgh.

In February 1332, at Greencastle, near the mouth of Lough Foyle, he had his cousin Sir Walter Liath de Burgh starved to death.

His widow, Maud (or Matilda), offered a reward for the capture of de Mandeville and his wife.

"[4] Maud fled to England, where she remarried, was again widowed in 1346, and then became an Augustinian canoness at Campsey Priory in Suffolk, where she is buried.