A lawyer, O'Connell served on the Montana Public Service Commission (1934-36). A member of the Democratic Party, O'Connell was elected to the 75th Congress (3rd January, 1937 - 3rd January, 1939). Over the next few years he played a leading role in the campaign to free Tom Mooney and Warren Billings. In 1937 O'Connell and James E. Murray introduced a resolution in the Senate calling on Governor Frank Merriam to pardon Mooney and Billings.
O'Connell and John Bernard were the only Congressmen to visit the International Brigades during the Spanish Civil War. O'Connell failed to be elected for the 76th Congress. He returned to Butte to practice law. He joined the Progressive Party but failed to be elected to Congress in 1948.
In 1950 O'Connell moved to Great Falls where he died on 16th January, 1956.