Gainer was a standout on the 1945 Normantown High School team, helping lead the Vikings to the State Basketball title during an era when there was only one class and over 300 high schools in the state. After a stint in the military, he came to Glenville State where he helped lead the Pioneers to the 1951 WVIAC Tournament title. He was the second leading scorer and top rebounder on that team.
 
Gainer was on a '51 squad that was loaded with Hall of Famers such as Bob "Hooks" Hardman, Dick Barrett, Don Merriman, Bob Turner, and Glennard Vannoy. Gainer made the All-Tournament Team that season.
 
After graduating from Glenville State, Gainer would go on to a be a long-time Gilmer County coach, teacher, administrator, and politician.