The Massachusetts Provincial Congress (1774–1780) was a provisional government created in the Province of Massachusetts Bay early in the American Revolution. Based on the terms of the colonial charter, it exercised de facto control over the rebellious portions of the province, and after the British withdrawal from Boston in March 1776, the entire province. When Massachusetts Bay declared its independence in 1776, the Congress continued to govern under this arrangement for several years. Increasing calls for constitutional change led to a failed proposal for a constitution produced by the Congress in 1778, and then a successful constitutional convention that produced a constitution for the state in 1780. The Provincial Congress came to an end with elections in October 1780.

The Province of Massachusetts Bay was a colony in New England which became one of the thirteen original states of the United States. It was chartered on October 7, 1691, by William III and Mary II, the joint monarchs of the kingdoms of England, Scotland, and Ireland, and was based in the merging of several earlier British colonies in New England. The charter took effect on May 14, 1692, and included the Massachusetts Bay Colony, the Plymouth Colony, the Province of Maine, Martha's Vineyard, Nantucket, Nova Scotia, and New Brunswick; the Commonwealth of Massachusetts is the direct successor. Maine has been a separate state since 1820, and Nova Scotia and New Brunswick are now Canadian provinces, having been part of the colony only until 1697.