The Michigan-born cleric, after brief service in Congregational and Presbyterian churches, early rejected the fundamentalism he learned at Chicago's Moody Bible Institute and, with it, all Christian orthodoxy. He adopted what he called “Christian Unitarianism” and developed it as a form of liberal religious humanism. Bradley nurtured the North Side's Peoples Church into a major Chicago institution until it numbered four thousand followers. He spread his message over the radio to a claimed five million listeners. The civic-minded pastor served on the Chicago Public Library board for a half century after 1925; the Cultural Center in the historic library building perpetuates his memory and name. His Peoples Church saw rapid decline after he ended his long service there in 1976, but his influence continued. Long the city's best-known non-Catholic religious leader, Bradley parlayed a charismatic personality, masterly rhetoric, and a civic sense into a career that attracted the support of citizens who did not agree with his theology.

Martin E. Marty