[1] After the end of hostilities, he joined the Graves Registration Service as a civilian, helping to locate the bodies of U.S. servicemen and either record their burial place or have the remains moved to a U.S. military cemetery.

[3] In 1920, Muir left the Navy and joined the United States Army, where he served as a port officer in France until 1922.

Howell G. Crim, Muir's longtime assistant chief usher, was named his replacement on April 4, 1938.

Muir joined the State Department on April 16, 1938,[9] as an assistant to Richard Southgate, chief of the International Conference Division.

[1][11] In 1942, he again served as the State Department representative aboard the MS Gripsholm, a Swedish ocean liner chartered by the U.S. government which exchanged more than 1,500 Japanese diplomatic, commercial, and other personnel and their families for 1,300 Americans.

[1][12] Muir was named Acting Ceremonial Officer in the State Department's Division of Protocol on July 27, 1943, and was promoted permanently into the position on March 20, 1944.

[13] In this position, Muir introduced new ambassadors and their credentials to the President of the United States, and handled any instance where someone with diplomatic immunity ran afoul of U.S.

While crossing the Rocky Mountains at high altitude, Muir suffered from breathing problems, which were later diagnosed as lung cancer.