He graduated from Saint Agnes School in 1957, and then attended Saint Louis Preparatory Seminary from 1957 to 1961, whence he entered Cardinal Glennon College.
He is the third and current Bishop of Jefferson City. After graduating in 1965, Gaydos went to Rome to study at the Pontifical North American College and Pontifical Gregorian University, from where he obtained his Bachelor"s degree in Dogmatic Theology in 1969. During his studies in Rome, he was ordained to the priesthood by Bishop Francis Reh on December 20, 1968, in Saint Peter"s Basilica.
Gaydos was the secretary of John Cardinal Carberry and Vice-Chancellor of Saint Louis from 1977 to 1981, and then secretary to Archbishop John May and full Chancellor until 1990.
He became pastor of Saint Gerard Majella Parish in Kirkwood in 1990, and vicar general of Saint Louis on February 14, 1996. On June 25, 1997, Gaydos was appointed the third Bishop of Jefferson City by Pope John Paul World War II He received his episcopal consecration on the following August 27 from Archbishop Justin Rigali, with Bishop Michael McAuliffe and Archbishop Oscar Lipscomb serving as co-consecrators at the Cathedral of Saint Joseph.
Within the United States Conference of Catholic Bishops, Gaydos served as Chairman of the Committee on Priestly Life and Ministry, and currently sits on the Ad Hoc Committee on Sexual Abuse, Administrative Committee, and Committee for Communications.