William Shirley (2 December 1694 – 24 March 1771) was a British colonial administrator who served as the governor of the British American colonies of Massachusetts Bay and the Bahamas. He is best known for his role in organizing the successful capture of Louisbourg during King George's War, and for his role in managing military affairs during the French and Indian War. He spent most of his years in the colonial administration of British North America working to defeat New France, but his lack of formal military training led to political difficulties and his eventual downfall.

Politically well connected, Shirley began his career in Massachusetts as advocate general in the admiralty court, and quickly became an opponent of Governor Jonathan Belcher. He joined with Belcher's other political enemies to bring about Belcher's recall, and was appointed Governor of Massachusetts Bay in Belcher's place. He successfully quieted political divisions within the province, and was able to bring about united action against New France when King George's War began in 1744. The successful capture of Louisbourg, which Shirley had a major role in organizing, was one of the high points of his administration.

After King George's War Shirley became mired in disputes over funding and accounting for the war effort, and returned to England in 1749 to deal with political and legal matters arising from those disputes. He was then assigned to a commission established by Great Britain and France to determine the colonial borders in North America. His hard-line approach to these negotiations contributed to their failure, and he returned to Massachusetts in 1753.

Military matters again dominated Shirley's remaining years in Massachusetts, with the French and Indian War beginning in 1754. Shirley led a military expedition to reinforce Fort Oswego in 1755, and became Commander-in-Chief, North America upon the death of General Edward Braddock.

Notably, as commander-in-chief, Shirley knew George Washington, who served under his command. In 1756, Shirley wrote a letter advocating in favor of a promotion for George Washington, writing, "I do therefore give it as my Opinion that Capt. Dagworthy who now acts under a Commission from the Governor of the Province of Maryland, and where there are no regular Troops join'd, can only take Rank as Provincial Captain and of Course is under the Command of all Provincial Field Officers, and in case it shall happen, that Colonel Washington and Capt. Dagworthy should join at Fort Cumberland. It is my Orders that Colonel Washington should take the Command."

His difficulties in organizing expeditions in 1755 and 1756 were compounded by political disputes with New York politicians, and over military matters with Indian agent Sir William Johnson. These disagreements led to his recall in 1757 as both commander-in-chief and as governor. In his later years he served as governor of the Bahamas, before returning to Massachusetts, where he died.

William Shirley, the son of William and Elizabeth Godman Shirley, was born on 2 December 1694 at Preston Manor in East Sussex, England. He was educated at Pembroke College, Cambridge, and then read law at the Inner Temple in London. In 1717 his grandfather died, leaving him Ote Hall in Wivelsfield and some funds, which he used to purchase a clerkship in London. About the same time, he married Frances Barker, with whom he had a large number of children. He was called to the bar in 1720. Although his inheritance had been substantial (about £10,000), he cultivated an expensive lifestyle, and suffered significant financial reverses in the depression of 1721. The financial demands of his large family (he and Frances had eight children by 1731) prompted him to seek an appointment in the North American colonies. His family was connected by marriage to the Duke of Newcastle, who became an important patron and sponsor of Shirley's advancement, and to that of Arthur Onslow, the Speaker of the House of Commons. Armed with letters of introduction from Newcastle and others (but no appointment), Shirley arrived in Boston, Massachusetts, in 1731.

Shirley was initially received with indifference by Massachusetts governor Jonathan Belcher, who refused him patronage positions that became available. In 1733 Shirley sought to secure from David Dunbar the commission as the crown surveyor general, but Dunbar eventually decided to retain the office. Influence from Newcastle eventually yielded Shirley a position as advocate general in the admiralty court. Belcher resisted further entreaties from Newcastle to promote Shirley, and Shirley began using his position to actively prosecute Belcher supporters whose illegal logging activities came under his jurisdiction.