Ka cika wannan magana: An haifi O'Brien a Jersey City, New Jersey, a ranar 7 ga Maris, 1879. Ya halarci Makarantun Jama'a na Jersey City, Kwalejin Kwalejin St. Aloysius da Kwalejin Saint Peter. Ya kammala karatunsa daga Jami'ar Fordham. Ya yi karatun doka a Makarantar Koyon Shari'a ta New York, an shigar da shi cikin mashaya kuma ya fara aiki a Jersey City. Ya kasance alkalin kotun aikata laifuka ta biyu, kuma shi ne darektan tsaron jama'a na Jersey City daga 1917 zuwa 1921. Ya kasance wakili ne ga
Babban Taron Jam'iyyar Democrat na 1920.