Born in Limestone, New York, Schoonmaker received an Artium Baccalaureus degree from Cornell University in 1891 and read law to enter the bar in 1894.

He was a captain in the Pennsylvania National Guard from 1912 to 1917, and was a lieutenant colonel in the United States Army from 1917 to 1919.

[1] On December 20, 1922, Schoonmaker was nominated by President Warren G. Harding to a new seat on the United States District Court for the Western District of Pennsylvania created by 42 Stat.

He was confirmed by the United States Senate on December 22, 1922, and received his commission the same day.

Schoonmaker served in that capacity until his death on September 5, 1945.