Piersol attended The Judge Advocate General's Legal Center and School at the University of Virginia and entered Judge Advocate General's Corps, United States Army, where he served in from 1965 to 1968.

He was in private practice in Sioux Falls, South Dakota from 1968 to 1993.

A member of the Democratic Party, he served in the South Dakota House of Representatives, serving as Minority Whip (1971 to 1972) and Majority Leader (1973 to 1974).

[1] On August 6, 1993, Piersol was nominated by President Bill Clinton to a seat on the United States District Court for the District of South Dakota vacated by Donald J. Porter.

He served as chief judge from 1999 to 2005 and assumed senior status on July 31, 2009.