Walter A. O'Brien, Jr. (December 19, 1914 – July 3, 1998) was a Progressive Party politician from Boston, Massachusetts, United States in the 1940s and the fourth child of Walter A. O’Brien from Portland and Susan Ann Crosby, both third generation Irish Americans. In 1949 O'Brien ran for mayor of Boston. Lacking sufficient financial support to pay for radio advertising, O'Brien commissioned campaign songs from local folk artists promoting his themes, recorded them, then played them out of a loudspeaker on a truck driven through town. O'Brien was fined $10 for disturbing the peace as a result.