He later transferred to the Judge Advocate General's Corps, and volunteered to serve in Europe during World War II.

He received the Bronze Star Medal for his wartime service, and he continued to serve until retiring as a colonel.

While in Congress, Pirnie was the ranking Republican member of the subcommittee that oversaw the 1969 draft for the Vietnam War.

After leaving Congress he practiced law in Utica and was president of a Mohawk, New York, clothing company from 1977 to 1980.

Pirnie was found behind the wheel of his car on the side of the road, and authorities presumed he had a heart attack and died while driving.