John King Mussio was born in Cincinnati, Ohio June 13, 1902, the son of John E. Mussio and Blanche (King) Mussio. He had one brother, Thomas J. Mussio. He was baptized and received his first communion in Sacred Heart Church in Cincinnati and attended Assumption Elementary School and St. Xavier High School, Cincinnati.
After completing his collegiate studies at Xavier University, he received a Master of Arts degree at the University of Notre Dame. From 1925 to 1930 he taught English at Xavier University and in the same period he studied law at the University of Cincinnati. He entered St. Gregory Seminary in 1920 and went from there to Mt. St. Mary Seminary for his theological studies.
After his ordination to the priesthood in Mt. St. Mary’s seminary chapel August 15, 1935, Bishop Mussio was stationed for a year at St. Louis Church, Cincinnati and for a short time he served as an instructor in a Cincinnati high school.
In September 1936 he was sent to the Angelicum in Rome where he was awarded a Doctorate in Canon Law, he returned to Cincinnati and was named assistant chancellor in August 1939. In January 1942, he became chancellor. In June of the same year he was raised to the rank of papal chamberlain with the rank of Very Reverend Monsignor.
On October 21, 1944 a new diocese was formed with Steubenville being named as the See City. On March 15, 1945 John King Mussio was named the first bishop. He was consecrated May 1, 1945 in Cincinnati. He retired October 11, 1977 and died April 15, 1978.