born in England of a family that had previously resided in the colonies, was brought at the age of nine to Boston, with which his later life is identified. After graduation from Harvard (1671), he was for a long time a tutor at the college, but in 1679 began his long political career, including such early offices as manager of the colony's printing press, deputy to the general court, and member of the Council (1684–86). While in England on business (1688–89), he aided Increase Mather in appealing to William III to recover the abrogated Massachusetts charter. Upon his return he resumed his position on the Council, and was a councilor of the new charter (1691–1725).
In 1692 he was appointed by Governor Phips as a special commissioner in the Salem witchcraft trials, in which he later regretted having participated, and in 1697, on a fast day set aside for repentance concerning errors in the trials, he was the only judge publicly to recant by standing in the Old South Church while the clergyman read his confession of error and guilt. After holding several judicial posts, he became chief justice of the superior court of judicature (1718–28), and despite his lack of legal training was considered a good and rather liberal jurist.
His various pamphlets give evidence of the many different matters in which he was interested. The Revolution in New England Justified (1691), written with Edward Rawson, is a loquacious but logical justification of the New Englanders who deposed Andros and resumed charter government in 1689. Phænomena quædam apocalyptica … (1697) is a prediction that New England will be the eventual seat of the New Jerusalem. The Selling of Joseph (1700) is an early antislavery appeal, and other works include A Memorial Relating to the Kennebeck Indians (1721), an early argument for humane treatment of the Indians. “Talitha Cumi” is an essay, not published until 1873, which argues against those who deny the resurrection of women.
Both as man and as author, Sewall is best remembered for the Diary, which was published by the Massachusetts Historical Society (3 vols., 1878–82), and which covers the period from 1674 to 1729, with a gap between 1677 and 1685, in an intimate and minute manner. Because he not only relates in detail the homely activities of Boston but also gives an honest revelation of his own character, he has been compared with his British contemporary, Samuel Pepys. He reveals, evidently unconsciously, the twilight of the Puritan tradition and the rise of the New England Yankee period, which transition he himself represented in his religious orthodoxy, tempered by an emphasis upon mercantilism in his capacity as a merchant. His practical Yankee bent made him less concerned with ideas and more with daily happenings. The thought in Cotton Mather's Diary thus receives a complementary balance for the student of the period in the journal of Sewall, which recounts such incidents as his unsuccessful wooing of Madam Winthrop with gifts of gingerbread, sermons, and a shilling and a half's worth of sugar almonds, and their disputes over the marriage settlement and whether he should wear a wig and keep a coach.