Purple angelica grows in eastern North America from eastern Canada and New England south to North Carolina and west to Minnesota, Iowa and Tennessee. It favours swampy, calcareous habitats with steady moisture. VASCAN lists it as native in Quebec and the Atlantic provinces. It is a host plant for black swallowtail and short-tailed swallowtail caterpillars, and small bees take nectar from the flowers.
The common names refer to the purple stems, and 'masterwort' to its historical use as a medicinal plant. Early American settlers boiled and candied the plant, and Europeans believed it could cure alcoholism. Wikipedia also records Indigenous medicinal and ceremonial uses, for example among Creek peoples.