He served in the United States Navy during World War II, from 1942 to 1945, achieving the rank of lieutenant.
[1] On September 28, 1970, Muir was nominated by President Richard Nixon to a new seat on the United States District Court for the Middle District of Pennsylvania created by 84 Stat.
He was confirmed by the United States Senate on October 8, 1970, and received his commission six days later.
[1] Muir presided over the trial of R. Budd Dwyer, the then Treasurer of Pennsylvania who was convicted in December 1986 of 11 counts of conspiracy, mail fraud, perjury and interstate transportation in aid of racketeering;[2] Dwyer was scheduled to be sentenced by Muir on those charges on January 23, 1987.
[3] Dwyer scheduled a press conference for the day before, January 22, where after stating his innocence, he killed himself in front of the gathered members of the media and his staff.