William Shirley (December 2, 1694 – March 24, 1771) is a British colonial administrator who is the longest-serving governor of the Province of Massachusetts Bay (1741–1749 and 1753–1756), then Governor of the Bahamas (1760–1768).

He is best known for his role in organizing the 1745 Siege of Louisbourg during King George's War, and for his role in military affairs during the French and Indian War.

He spends most of his years in the colonial administration of North America working to defeat New France, but his lack of formal military training leads to political difficulties and his eventual downfall.

Politically well connected, Shirley begins his career in Massachusetts as advocate general in the admiralty court, and quickly becomes an opponent of Governor Jonathan Belcher.

He joins with Belcher's other political enemies to bring about Belcher's recall, and is appointed Governor of Massachusetts Bay in Belcher's place.

He successfully quiets political divisions within the province, and is able to bring about united action against New France when King George's War begins in 1744.

The successful Siege of Louisbourg, which Shirley has a major role in organizing, is one of the high points of his administration.

After King George's War Shirley becomes mired in disputes over funding and accounting for the war effort, and returns to England in 1749 to deal with political and legal matters arising from these disputes.

He is next 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 contributes to their failure, and he returns to Massachusetts in 1753.

Military matters again dominate Shirley's remaining years in Massachusetts, with the French and Indian War beginning in 1754.

Shirley leads a military expedition to reinforce Fort Oswego in 1755, and becomes Commander-in-Chief, North America upon the death of General Edward Braddock.

His difficulties in organizing expeditions in 1755 and 1756 are compounded by political disputes with New York politicians, and over military matters with Indian agent Sir William Johnson.

These disagreements lead to his recall in 1757 as both Commander-in-Chief and as governor.

In his later years he serves as governor of the Bahamas, before returning to Massachusetts, where he dies.