Georgetown University Law Center.
He received his Bachelor of Arts from College of the Holy Cross and his masters and law degree from Georgetown University. He later served as City Corporation Counsel and as a New York Surrogate Court judge. Shortly after the surprise resignation of Mayor Jimmy Walker in 1932, Tammany Hall nominated O"Brien for mayor in a special election, and he beat write-in candidate (and Acting Mayor) Joseph V. McKee by more than half a million votes.
O"Brien"s inauguration was held in the Hall of Records, at 31 Chambers Street in Manhattan, and was devoid of the pageantry that had greeted many of his predecessors.
His inauguration speech did not outline a vision for the city, but rather, reflected on the work of the court and the legal profession in general. In the post inauguration news conference, the new mayor was asked who would be the new police commissioner.
"I don"t know" O"Brien answered. "They haven"t told me yet."
Although he is credited with expanding the city"s ability to collect taxes, restoring order to the city"s finances, and trimming the budget, O"Brien was defeated for re-election in a three-way race by the colorful Republican-City Fusion Party candidate, Fiorello H. Louisiana Guardia, in November 1933.
He served just one year in office.
O"Brien returned to his legal work and served three times as a delegate to the Democratic National Convention. He died on September 21, 1951 at his home at 40 East 75th Street at 7:25 p.m. He was buried in the Gate of Heaven Cemetery in Westchester County.