Mitchell did not start running track until he was in high school. He attended Crest High School in Shelby, North Carolina. After high school he gained an athletic scholarship at Western Carolina University where he broke numerous school records and reached the NCAA Outdoor Championship three out of four years. Mitchell holds personal bests of 21.13 & 46.17 (indoors) and 20.43 & 44.96 (outdoors). He was also initiated as a member of Alpha Phi Alpha Fraternity while at Western Carolina. Mitchell currently resides in Cullowhee, North Carolina. He is currently being coached by Danny Williamson. His agent is Andy Stubbs and he is being sponsored by Under Armour. 
At the 2012 United States Olympic Trials, Mitchell qualified for the Olympic team by finishing fifth in the 400 metres with a time of 44.96, which qualified him to run in the 4x400 metres relay as a member of the U.S. relay team. At the 2012 Summer Olympics held in London, Mitchell ran the first leg of the heat for the 4x400 metres relay and revealed afterwards that he broke his left fibula at the 200m mark. Despite this, Manteo finished his lap and clocked a time of 46.1, and the American team was able to qualify for the final. Mitchell later earned a silver medal after the American team placed second in the final.