William Freeborn (1594–1670) was one of the founding settlers of Portsmouth on Aquidneck Island, having signed the Portsmouth Compact with 22 other men while still living in Boston. Coming from Maldon in Essex, England, he sailed to New England in 1634 with his wife and two young daughters, settling in Roxbury in the Massachusetts Bay Colony. He soon moved to Boston where he became interested in the preachings of the dissident ministers John Wheelwright and Anne Hutchinson, and following their banishment from the colony during the Antinomian Controversy, he joined many of their other followers in Portsmouth.

The Antinomian Controversy, also known as the Free Grace Controversy, was a religious and political conflict in the Massachusetts Bay Colony from 1636 to 1638. It pitted most of the colony's ministers and magistrates against some adherents of Puritan minister John Cotton. The most notable Free Grace advocates, often called "Antinomians", were Anne Hutchinson, her brother-in-law Reverend John Wheelwright, and Massachusetts Bay Governor Henry Vane. The controversy was a theological debate concerning the "covenant of grace" and "covenant of works".