Robert Shannon was of mixed ethnicity, born to a white mother and black father. As a youth in Seattle, he lived in a primarily black district, and often fought on the streets because the other boys thought he was white. His family then moved to Lynnwood, Washington, where he again often fought because the white kids thought he was black. He began boxing competitively and won a US junior title at age 15, and a world junior title at age 16. Shannon qualified for the 1980 US Olympic team that did not compete.
Shannon was 1980 AAU Champion, 1982 US Amateur Champion, and 1984 US Golden Gloves Champion. He lost his second bout at the 1984 Olympics and then turned professional, going undefeated in his first 15 fights, with two draws. However, his career then began to slide, and Shannon retired in 1990 with a pro record of 18 wins, 6 losses, and 2 draws. He never fought for any major titles. Shannon later worked as a barber and a boxing trainer, running his own gym.