He received a bachelor's degree from Princeton University in 1936, graduating from Harvard Law School in 1939.
In building his collection, Gregory worked closely with Mary Allis, from whom he purchased numerous pieces;[1] he also purchase work from Adele Earnest;[2] the Earnest-Gregory Dovetailed Goose, a decoy which both collectors owned, now bears their name.
[3] Eventually his collection came to contain, in addition to decoys, weathervanes, hooked rugs, tinware, watercolors, and other items, among them portraits by John Brewster Jr., Erastus Salisbury Field, and Ammi Phillips.
Chairman of the Wilton Historical Society, Gregory converted an eighteenth-century barn into a home where he could show off his pieces.
A vice president and trustee of the American Folk Art Museum from 1964, in 1972 the museum exhibited his collection in the exhibit "An Eye on America: Folk Art from the Stewart E. Gregory Collection".