Chief Judge Rubén Castillo of Chicago, Illinois, received his Bachelor of Arts in Political Science from Loyola University Chicago in 1976 and his law degree from Northwestern University School of Law in 1979.

On January 27, 1994, President Clinton nominated Chief Judge Castillo to the United States District Court for the Northern District of Illinois as an Article III federal judge. In 1999, President Clinton nominated him to be the vice-chair of the United States Sentencing Commission. Chief Judge Castillo has also served as an adjunct professor of trial advocacy at Northwestern University School of Law for more than twenty years. As a result of his work with students, he has received five teaching awards from Northwestern Law students.

In 2012, for a term of three years, his fellow judges in the Seventh Circuit designated him to serve as a member of the Judicial Conference of the United States Courts, the policy making body of the federal court system.

On July 1, 2013, he assumed the position of Chief Judge of the United States District Court for the Northern District of Illinois.