Agase grew up in Illinois and attended the University of Illinois, where he was a standout as a guard starting in 1941. He was named an All-American in 1942. Agase then entered the U.S. Marines during World War II and played a season at Purdue while in training. He was again named an All-American in 1943. After his discharge from the Marines, he came back to Illinois and played a final season in 1946, after which he was named an All-American for a third time. Agase began his professional football career with the Los Angeles Dons of the All-America Football Conference (AAFC) in 1947, but was soon traded to the Chicago Rockets and then the Browns, where he remained until 1952. Cleveland won two AAFC championships and one National Football League championship while Agase was on the team. After retiring from football, Agase worked as an assistant coach for the Dallas Texans and, after a brief return to playing for the Baltimore Colts, Iowa State University. He was hired as an assistant at Northwestern in 1956 under head coach Ara Parseghian.