Born in Cork, Ireland March 21, 1821, he was brought to the Philadelphia by his parents when he was two years old. Descended from British General William O'Sullivan, he eventually settled in Cincinnati. He was a U.S. Army Officer (Major) in the war with Mexico and Brevet Brigadier General Civil War veteran, serving with the 48th OVI. He was wounded at the battle of Shiloh. A Catholic attorney, he fought against the bigotry of the "Know Nothings". After the Civil War President Johnson appointed him as U.S. Minister to Columbia.
He died March 2, 1883 and is buried at Spring Grove Cemetery, Cincinnati, Hamilton County, Ohio, USA. Plot: Section 20, Lot V. His wife was Margetta Sullivan.