Trained as an architect, Stein participated in several of the most influential housing complex designs of the 20th century, including the "garden city" plans for Sunnyside Gardens in Queens, New York; Radburn, New Jersey; Chatham Village in Pittsburgh; and Baldwin Hills Village (known today as Village Green) in Los Angeles. He attended both Columbia University and the Ecôle des Beaux Arts.
In 1921, he and Henry Wright developed a partnership rooted in Ebenezer Howard’s "Garden City" ideals of safe, community-based housing. With Wright, Lewis Mumford, and other colleagues, Stein founded the Regional Planning Association of America in 1923 envisioning widespread reform of U.S. planning and design practices, focusing on high-density urban housing and the residential subdivision. Their designs were successful in great part because of their emphasis on the landscape. For example, Sunnyside Gardens provided central courtyards where families could gather while the suburban locale of Radburn led to experimentation with peripheral roads and short automobile-friendly culs-de-sacs with a variety of housing unit types. Stein later served with Reginald Johnson as consulting architects for the design of Baldwin Hills Village, in Los Angeles. Stein also authored Toward New Towns for America.
The joint work of Stein and Wright changed the way towns are planned, with significant advancements in the methods, policies, and theories undergirding contemporary planning efforts.