Moved to Boston (c. 1719) with parents and siblings. No profession; in spite of moral qualms about slavery, Vassall lived on proceeds of Jamaica sugar plantations he inherited from his father. Visited Jamaica (1747-c. 1750). Presented a set of twelve anatomical drawings to Harvard College (1750). Held few civic offices, as he was reluctant to accept low- ranking posts. Spent much of 1750s engaged in a complicated multilateral slander suit. Sympathetic to British government; moved to London (1775). Later involved in lawsuits to recover Massachusetts and Rhode Island property that had been seized in Revolutionary War.
Son of Leonard and Ruth (Gale) Vassall of Jamaica. Educated at Harvard (B.A. 1733). Married (1) Ann Davis; (2) Margaret Hubbard (1760). Sixteen children. Died in London.