McManus was nominated by President John F. Kennedy on June 23, 1962 to a seat on the United States District Court for the Northern District of Iowa vacated when Judge Henry N. Graven assumed senior status. He was confirmed by the United States Senate on July 13, 1962, and received his commission on July 16, 1962. He had not lived in the Northern District until this appointment, and thus needed to relocate from Keokuk (in Iowa's far southeastern county) to Cedar Rapids, Iowa. He served as Chief Judge from 1962 to 1985. He assumed senior status on February 9, 1985.[1] No federal district court judge in Iowa history served for a longer period on the bench than McManus. He died at the age of 97 on March 20, 2017, in Cedar Rapids;[2] at the time of his death, McManus was the longest serving living federal judge.[3][4]