William Robert FitzGerald, 2nd Duke of Leinster, KP, PC (Ire) (12/13 March 1749 – 20 October 1804) was an Irish liberal politician and landowner.

FitzGerald then sat in the Irish House of Commons for Dublin City until 1773, when he inherited his father's title and estates.

In 1770, FitzGerald was chosen Grandmaster of the masonic Grand Lodge of Ireland, which post he held for two years.

He was also the elder brother of the 1790s revolutionary Lord Edward FitzGerald, and was a first cousin of the English liberal politician Charles James Fox.

His family's estates of 60,000 acres (25,000 Ha) in Kildare were in three main parts, around Maynooth, Rathangan and Athy.