Kinnamon graduated from Lincoln High School and the University of Nebraska, where he earned a degree in business administration. He married Thelma Lorraine Johnson on April 29 1945. He began his umpiring career in the Sooner State League in 1953, moving up to the Pioneer League (1954), the Eastern League (1955-56) and the American Association (1956-60) before joining the AL staff in September 1960. He was the home plate umpire when Roger Maris hit both his 60th and 61st home runs in to break Babe Ruth's single-season record. After retiring from field duties due to a June 1969 injury, Kinnamon became an umpiring supervisor, and then the chief instructor in the major leagues' new Umpire Specialization Course, which later became the Umpire Development Program. He eventually began running the training program independently, operating one of the two principal umpiring schools from 1974 to 1981 in St. Petersburg, Florida before selling the school to umpire Joe Brinkman, who had been an instructor in Kinnamon's program since 1973. A resident of Daytona Beach, Florida throughout his major league career, Kinnamon later relocated to Largo, Florida.