Bellmon was born in Tonkawa, Oklahoma, and graduated from Billings High School in Billings, Oklahoma. He graduated from Oklahoma A &amp; M (now Oklahoma State University) in 1942 with a bachelor's degree in agriculture. He was a lieutenant in the United States Marine Corps from 1942 to 1946. He was a tank platoon leader in the Pacific Theater of World War II. He took part in four amphibious landings on Pacific islands, including Iwo Jima. For his service, he was awarded the Legion of Merit and a Silver Star. After the war he returned to farming and took up politics.