Ellenson was born in Wisconsin, grew up in Miami, and attended the University of Georgia, where he was a starting Tackle on the Bulldog's 1942 national championship football team.

[2] He was a starting senior lineman on the 1942 Bulldogs team that finished 11–1 and defeated the UCLA Bruins in the Rose Bowl, thus claiming a share of the 1942 national championship.

During the Battle of the Bulge in December 1944, he was an infantry lieutenant who commanded the defense of a hill against repeated assaults by elements of the German army.

[3][4][5] Following his discharge from the U.S. Army, Ellenson played professionally for the Miami Seahawks of the All-America Football Conference (AAFC) for a single season in 1946.

After the Gators struggled to a 1–2 record to begin the 1962 season, Ellenson wrote a letter to each member of the team detailing his World War II experiences and encouraging them to play harder: "You'll be a better man for it, and the next adversity won't be so tough."

Players and coaches credit "The Letter" for inspiring the team to beat several tough opponents and end the season with a bowl victory.

He delivered a memorable pep talk to the team using his favorite "positive molecules" metaphor, and the Gators upset the top-ranked Houston Cougars to win the NCAA tournament—the first national championship, in any sport, won by University of Florida athletes.

In 1986, then-Gators coach Galen Hall invited Ellenson to give a pregame talk before the 3–4 Gators faced the 7–0 and 5th-ranked Auburn Tigers.

[15] When Spurrier returned to his alma mater in 1990 to become the Gators' head coach, he again invited Ellenson to deliver inspirational talks before big games.

[18][19] In 1991, coach Steve Spurrier established the Gene Ellenson Award, which is given annually to the "most inspirational player" on Florida's football team.