O'Brien was appointed in 1952 by John F. Kennedy to serve in Massachusetts as the director of his successful U.S. Senate election campaign and, in 1958, to serve in Massachusetts as the director of his successful reelection campaign.
В 1952 году он был назначен Джоном Ф. Кеннеди руководителем в Массачусетсе его впоследствии успешной избирательной кампании в Сенат США.