After attending Columbia College Law School, he was admitted to the bar of New York in 1889.

He remained a Representative until 1919, having declined to run in 1918 in order to seek (unsuccessfully) election as a U.S.

O'Shaunessy then was appointed by President Woodrow Wilson collector of internal revenue for the district of Rhode Island.

He served in that position until Wilson left office in 1921, when he returned to the practice of law.

He was buried in St. Francis Cemetery in Pawtucket, Rhode Island.