William Shirley was born on December 2, 1694, at Preston in Sussex, England, the son of William Shirley and Elizabeth Godman. His family belonged to the respectable gentry but did not possess the wealth required to guarantee a life of leisure. Shirley was educated for the law and entered the Middle Temple in London. Legal study trained him in argument, administration, and the workings of royal government, skills that later proved more important to his career than battlefield experience.

He married Frances Barker in 1717, and the couple eventually had a large family. Seeking better opportunities, Shirley emigrated to Massachusetts in 1731. He established a legal practice in Boston and became active in disputes concerning land titles and the boundary between Massachusetts and neighboring colonies. His work brought him to the attention of imperial officials and demonstrated a talent for presenting colonial interests in language persuasive to ministers in London.

Shirley was appointed royal governor of Massachusetts in 1741. He quickly confronted the pressures of King George’s War, the North American extension of the War of the Austrian Succession. Although he had no formal military education, he championed an audacious colonial expedition against Louisbourg in 1745. He helped secure legislative support, troops, money, ships, and cooperation from other colonies. The fortress’s capture greatly enhanced his reputation and convinced him that coordinated colonial forces could strike major French positions.

After the war, Shirley traveled to Britain to defend Massachusetts interests and continued developing plans for imperial expansion. He became deeply involved in diplomacy with the Haudenosaunee and in proposals to strengthen Oswego and challenge French influence in the Great Lakes. By 1754 he was one of the most experienced royal governors in British America: ambitious, energetic, skilled at planning, but sometimes overly confident that complicated campaigns could be directed through political negotiation and written instructions.