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 Siege 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. 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.