Born in Chicago, Illinois, Andersen received a Bachelor of Arts degree from Harvard University in 1967 and a Juris Doctor from the University of Illinois College of Law in 1970.

He was an administrative assistant to Majority Leader Henry Hyde in the Illinois House of Representatives from 1970 to 1972.

Andersen then entered private practice in Chicago until 1980.

He was a judge on the Circuit Court of Cook County, Illinois from 1984 to 1991, and a Supervising Judge, Chicago Traffic Court, Chicago, Illinois from 1989 to 1991.

[1] On July 24, 1991, Andersen was nominated by President George H. W. Bush to a seat on the United States District Court for the Northern District of Illinois vacated by Stanley Julian Roszkowski.