Born in Hewitt, Minnesota, Shanstrom received a Bachelor of Arts degree from the University of Montana in 1956, a Bachelor of Science degree from the University of Montana in 1957, and a Bachelor of Laws from the University of Montana School of Law in 1957.

He was a United States Air Force first lieutenant, JAG Corps from 1957 to 1960.

He was nominated by President George H. W. Bush on February 23, 1990, to a seat on the United States District Court for the District of Montana vacated by Judge James F. Battin.

He assumed senior status on January 30, 2001, due to a certified disability,[2] and retired into inactive senior status on September 15, 2013, meaning that while he remained a federal judge, he no longer heard cases or participated in the business of the court.

[3] Shanstrom died on January 13, 2020, at his home in Palm Desert, California of the effects of Parkinson's disease.