University of Michigan Law School.
O"Brien was a lawyer by profession and a Republican politician. In 1883 he was an unsuccessful candidate for the office of Justice of the Michigan Supreme Court. In 1896 and 1904 he was a delegate to the Republican National Convention from Michigan.
O’Brien, a graduate of the University of Michigan law school, held the following posts as ambassador of the United States:
Denmark, 1905–1907 (appointed by President Theodore Roosevelt)
Japan, 1907–1911 (appointed by President Theodore Roosevelt)
Italy, 1911–1913 (appointed by President William Howard Taft)
O’Brien died on May 19, 1933.