William Petty Fitzmaurice was born on May 2nd, 1737 in Dublin, Ireland. Petty's earlier education was largely neglected. He was taught by a tutor and attended a local school in Dublin. When he was 14 he was sent to Oxford where after two years his father purchased a commission for him in the British Army. He shipped off to the continent during the 7 years war and at the Battle of Minden he distinguished himself. His role in politics began without him, when in 1760 he was elected to the House of Commons as the member form his families borough in Buckinghamshire. He was not that interested in the seat and continued on in his role as aide-de-camp for King George II. He was elected to the same seat in the 1761 election but was not to sit in the House of Commons due to the fact that his father died that same year and Petty inherited his title of the Earl of Shelburne and his seat in the House of Lords. Shelburne was offered the position of Secretary of State for Trade by Bute, but choose instead to serve as President of the Board of Trade. His obvious quest for high office alienated many of his colleagues. In 1763 he made an attempt to tie himself to William Pitt and force Bute to replace Grenville with Pitt.

 This and his backing of John Wilkes against King George II forced him from power and into early retirement. He took up residence at his county estates but was to shortly take his seat in the Irish House of Lords. Within the year he was back in favour and  although he refused the position of President of the Board of Trade in Rockingham's ministry, due to the colonial policies, he did take up the role of Secretary of State for the Southern Department in Chatham's ministry.

In 1771, after the death of his wife, he travelled to the continent with his friend Isaac Barre, who was also weary about Britain's policies towards the American colonies. He spoke out against confrontation with the colonies and supported the withdrawal of troops from American in order to defuse the situation. Chatham passed away in 1778, after the war in America had begun, and Shelburne was able to secure the support of Chatham's supporters.

This was not enough to help him gain power due to his previous reputation during Bute's ministry which had earned him a reputation of someone who should not be completely trusted. He remarried in 1779 and in 1782 he accepted a position in the 2nd Rockingham Ministry as Secretary of State for the Home Department.

When Rockingham died later that year Shelburne was elevated to the office of the Prime Minister. Shelburne quickly pursued a policy of ending the war in America, which he believed should have never been fought, and tried to form a broad coalition with the support of many segments of Parliament. He worked to make government more efficient and implement the principles of  free enterprise into his governments economic policy. 

Within the year North and Charles James Fox, under the Duke of Portland were able to pull together enough support to oppose Shelburne and force him from office. He left Parliament and although a member of the House of Lords he effectively withdrew from politics and lived until 1805 when he passed away on May 7th.