He was an Assistant United States Attorney of the Northern District of Illinois from 1963 to 1966, returning to private practice from 1966 to 1983.
[1] On November 23, 1982, Plunkett was nominated by President Ronald Reagan to a seat on the United States District Court for the Northern District of Illinois vacated by Judge James Benton Parsons.
Plunkett was confirmed by the United States Senate on December 10, 1982, and received his commission the same day.
He assumed senior status on July 10, 1998, due to a certified disability.
He was in inactive senior status, meaning that while he remained a federal judge, he no longer heard cases or participated in the business of the court.