Dewar attended Indiana University, where he was a standout as a halfback on the school's football team starting as a sophomore in 1942.

[1] He ran back a punt 90 yards for a touchdown in a 53–0 victory over Butler University that year.

[1] Dewar joined the U.S. Army in 1943 during World War II and played service football at Camp Grant in Rockford, Illinois.

[5] He instead joined the Cleveland Browns of the All-America Football Conference, who had selected him in the 1947 AAFC Draft along with former Indiana teammate Bob Cowan.

[6][7] The Browns finished the 1947 season with a 12–1–1 record and won the AAFC championship against the New York Yankees.