He was born in on a cattle ranch near Kent, Kansas to John E. O'Sullivan and Josephine Kluh O'Sullivan on May 31, 1883. He was married to Ellen Katherine Lovely. He graduated from Christian Brothers College, in St. Joseph, Missouri, attended St. Benedict’s College, in Atchison, Kansas in 1904 and 1905 and graduated from Creighton University's Law School in Omaha, Nebraska in 1910. He was admitted to the bar in 1910 and set up practice in Omaha.
He ran for governor of Nebraska in 1934 but was unsuccessful in getting the Democratic nomination and was also unsuccessful as a write-in candidate in 1934 for the United States Senate. He was a delegate to the Democratic National Conventions in 1924, 1928, 1932, 1940, and 1944. He was elected as a Democrat to the Eighty-first United States Congress serving January 3, 1949 to January 3, 1951. He unsuccessfully ran for reelection in 1950 to the Eighty-second United States Congress. He resumed the practice of law and died in Omaha on February 7, 1968. He is buried in Calvary Cemetery, in Omaha.