While attending Tennessee State University, Mims became the first African-American woman to compete in the 800 meters and the first American to win Olympic gold at the 1968 Games in Mexico City. From 1967 to 1980, she won 10 national indoor and outdoor titles and set several American records. Her fastest 800-meter time, 1:57.9 in 1976, was a long-standing American record in the event. Today, being an "overcomer" informs Mims's work as an motivational speaker and chaplain for the U.S. Olympic team. She is also the founder and president of the United States Council for Sports Chaplaincy.