William FitzWilliam, 4th Viscount FitzWilliam (1748–1833), was an Anglo-Irish nobleman and politician. He was born into a prominent family and inherited the title of Viscount FitzWilliam in 1816. FitzWilliam served as a member of the House of Lords and was known for his involvement in various political matters during his lifetime. FitzWilliam was also a significant landowner in Ireland, particularly in County Wicklow. He was recognized for his contributions to agriculture and local development. His legacy includes the promotion of social and economic improvements in the regions he managed, reflecting the responsibilities of the aristocracy during his era.