Mitchell came to the Virginia from the Charlotte Christian School in Charlotte, North Carolina as a lightly-regarded recruit, choosing the Cavaliers over offers from Navy and George Washington. He had an inconsistent freshman season in 2010–11, but played more than expected after an injury to star Mike Scott.
He joined Scott and classmate Joe Harris in the Cavaliers' starting lineup midway through the 2011–12 season as the trio led the team to a 22–10 record and the program's first NCAA Tournament appearance in five years. As a junior the next year, Mitchell averaged 13.1 points and 8.9 rebounds per game, earning third-team All-Atlantic Coast Conference honors. With more support as a senior, Mitchell's personal statistics declined, but the Cavaliers enjoyed one of their best seasons in years, recording a 30–7 record, winning both the regular-season and ACC Tournament championships and earning a top seed in the 2014 NCAA Tournament. Mitchell was named to the ACC All-Defensive team and second-team All ACC Tournament.
After going undrafted in the 2014 NBA draft, Mitchell joined the Houston Rockets for the 2014 NBA Summer League. On September 26, 2014, he signed with the Rockets, but was later waived by the team on October 23. On November 2, 2014, he was acquired by the Rio Grande Valley Vipers of the NBA Development League as an affiliate player of the Rockets. In 49 games for the Vipers in 2014–15, he averaged 9.8 points, 9.0 rebounds, 1.6 assists and 1.0 steals per game.
In July 2015, Mitchell joined the Brooklyn Nets for the 2015 NBA Summer League. On August 13, 2015, he signed with Olympique Antibes for the 2015–16 LNB Pro A season. In 34 games for Antibes, he averaged 9.2 points, 7.2 rebounds and 1.6 assists per game.
In July 2016, Mitchell joined the New York Knicks for the 2016 NBA Summer League. On August 30, 2016, he signed with the New Zealand Breakers for the 2016–17 NBL season. On January 26, 2017, Mitchell fell to the floor in agony early in the fourth quarter of the Breakers' 94–81 loss to the Cairns Taipans after what seemed to be an innocuous poke to the face while contesting a rebound with Taipans centre Nnanna Egwu resulted in his left eyeball coming out of its socket. Mitchell was taken to Auckland Hospital after the incident. Breakers general manager Dillon Boucher was advised by specialists that while there was some damage to his eye, "the early reports are very positive that the injury is not as serious as first feared." Mitchell was later discharged by specialists that night and reported having vision in the eye. On February 7, 2017, he returned to the US to seek further specialist advice on his injured eye. In 25 games for the Breakers, Mitchell averaged 9.5 points, 7.2 rebounds and 2.1 assists per game.
On February 24, 2017, Mitchell was acquired by the Long Island Nets of the NBA Development League.
In May 2016, Mitchell trialled for the Panama national basketball team ahead of the 2016 Centrobasket in June. He made the squad, and in six games for Panama, he averaged 5.0 points, 5.5 rebounds, 1.8 assists and 1.0 steals per game.