One of the top 50 players out of Texas in the 2013 recruiting class, Thomas decided to sign with Oklahoma so that he was close to home. He played in every game as a true freshman, starting the final four games at corner (32 tackles, five pass breakups). Thomas ended the year on a high note, breaking up three passes and making four stops against Clemson in the Russell Athletic Bowl. Big 12 coaches named him second-team all-conference the next fall, starting 11 of 12 games played and posting 46 stops, five interceptions, and four pass breakups. Thomas achieved first-team all-league accolades as a junior full-time starter, tying for fourth nationally with 19 passes defensed. Two of those plays were interceptions, and he also had 46 tackles, two for loss, on the year. His game fell off a bit in 2017, however, making 27 tackles, two for loss, one interception, and two pass breakups in 12 games. Thomas started the first nine games of the year, then missed two games and played minimal snaps in three others due to a knee injury. Thomas has had some disciplinary issues during his college career. He was suspended for disciplinary reasons twice in 2015, for the first quarter of the season opener and for a full game two weeks later. In December 2015, Thomas was arrested for failing to appear in court for a traffic citation. Before the 2016 season, Thomas was arrested after running from the scene of a bar fight (he ran because of the night he spent in jail).