Interrupting his legal education to serve in the American Civil War, he was an assistant paymaster in the United States Navy from 1862 to 1865 aboard the USS Housatonic (sunk by the submarine torpedo, H.L.

Following the war, he relocated to Iowa, where he read law to enter the bar in 1866.

[1][2] Woolson received a recess appointment from President Benjamin Harrison on August 14, 1891, to a seat on the United States District Court for the Southern District of Iowa vacated by Judge James M. Love.

He was confirmed by the United States Senate on January 11, 1892, and received his commission the same day.

His service terminated on December 4, 1899, due to his death in Des Moines, Iowa.