William FitzWilliam, 3rd 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 was known for his role in the British Parliament, where he served as a member of the Whig Party and was involved in various political issues of his time. In addition to his political career, FitzWilliam was a significant landowner in Ireland and England. He was also recognized for his contributions to agriculture and social reform, promoting improvements in farming practices and advocating for the welfare of the local population on his estates.