William Fairfax was born in London in 1691, the son of Henry Fairfax and grandson of Henry Fairfax, fourth Lord Fairfax of Cameron. He belonged to a distinguished English family but not to the branch possessing the greatest wealth. As a younger son, William could not rely upon inheriting a major estate and instead pursued advancement through naval, commercial, and colonial service. This circumstance made his upbringing aristocratic in connection but practical in direction. Details of his formal schooling are limited, though his later work shows strong literacy, accounting ability, and administrative competence. He entered royal naval service as a young man and learned the discipline, navigation, logistics, and hierarchy of Britain’s maritime world. Service carried him far from England and introduced him to the Atlantic empire in which he would spend most of his life. Fairfax held positions in the Bahamas, including customs and judicial responsibilities, and married Sarah Walker, the daughter of a colonial official. Their children were born within this mobile imperial environment. After Sarah’s death he married Deborah Clarke. His duties later took the family to New England, where he worked as a customs collector at Salem and Marblehead. The decisive family connection was his relationship with his cousin Thomas, sixth Lord Fairfax, proprietor of Virginia’s Northern Neck. William became the proprietor’s agent and moved to Virginia in the 1730s. He first lived near the lower Potomac and then established Belvoir plantation in Fairfax County. There he supervised land business, served on the governor’s Council, and entered the colony’s planter elite. Belvoir’s wealth depended upon enslaved labor.