From the Massachusetts Historical Society -- The first documented reference to the slave trade in Massachusetts is in the journal of John Winthrop (the founder of Boston), who recorded on 26 February 1638 that the Massachusetts ship Desire had returned from the West Indies carrying "some cotton, and tobacco, and negroes, etc., from thence..." (Dunn et al, eds., Journal, 1996, p. 246). Massachusetts and Rhode Island were the principal slave trading colonies in New England, and Boston was one of the primary ports of departure for slave ships. Slaveholding was significant economically in Rhode Island where there were sizable plantations using slave labor. In Massachusetts, slaveholding probably was of limited economic importance except in Boston where craftsmen used slaves in their trades, but the slave trade out of Boston was much more significant. The height of the New England slave trade is generally considered to be during the period 1740-1769.
In 1644 Boston merchants began importing slaves directly from Africa, selling them in the West Indies, and bringing home sugar to make rum, initiating the so-called triangular trade. From 1672-1696 the British Parliament granted the Royal African Company a monopoly in the slave trade. Yankee slavers avoided the monopoly by smuggling slaves in through small coastal harbors. In 1681, John Saffin and other Boston merchants wrote to the shipmaster William Welstead, warning him that the authorities planned to seize a slave ship heading for Rhode Island, and that he should intercept the vessel and direct it to Nantasket to offload its human cargo. In 1696 the British Parliament revoked the monopoly held by the Royal African Company, enabling Massachusetts merchants and shipmasters to engage freely in the slave trade.
Colonial governors in the eighteenth century were specifically forbidden to assent to any law laying duties on or discouraging the slave trade (Greene, p. 24). There were some attempts to regulate or even to eliminate the slave trade, but most were ineffective or of short duration. A miscegenation act of 1705-1706 included a £4 import duty on slaves brought into the colony, but an owner could recoup his expenses if a slave were sold out of the colony within a year, or if the slave died within six weeks of import. It has been argued that this act, rather than curtailing the slave trade, was simply a revenue-raising endeavor for the colony (Greene, p. 56).
Hugh Hall, originally from Barbados, was a wealthy commission merchant in Boston who carried on a significant trade with his island homeland, part of which involved importing slaves from Barbados to Boston.Detail of Hugh Hall Account Book, page 27 His account book for the years 1728-1733 contains pages (pp. 5, 6, 8, 9, 27, 28, 29, 30, 31, 34, 35, 36) with entries concerning slaves and their purchasers. Hall often noted when slaves died, or were sold out of the province, probably so that he could recover the costs of import duties.
Other, heavier duties were proposed at various times through the eighteenth century, but they were either voted down, or took effect for only a year. For example, a 1767 bill (March 1767 manuscript copy, April 1767 manuscript copy) to impose a duty of £40 on the importation of slaves into Massachusetts, was "unanimously non-concurred" (voted down) in the House. [https://www.masshist.org/endofslavery/index.cfm?queryID=60]