Wallace did not see any action in his Freshman and Sophomore years at Alabama. He earned a walk-on scholarship before his Junior year in 2016. In 6 games, Wallace totaled 11 tackles. During his senior year, Wallace started in 14 games. He was a starter during the 2018 College Football Playoff National Championship game, where Alabama won in overtime over Georgia, 26-23. Wallace totaled 48 tackles and caught 3 interceptions in his senior year.
On May 1, 2018, the Buffalo Bills signed Wallace to a three-year, $1.71 million contract as an undrafted free agent. Throughout training camp, Wallace competed for a roster spot as a backup cornerback against Taron Johnson, Ryan Carter, Breon Borders, and Lafayette Pitts. On September 1, 2018, the Buffalo Bills waived Wallace as part of their final roster cuts, but signed him to their practice squad the following day. On November 6, 2018, the Buffalo Bills promoted Wallace from their practice squad to the active roster after releasing Phillip Gaines. On November 11, 2018, Wallace made his professional regular season debut and first career start and made one tackle and a pass deflection during a 41-10 victory at the New York Jets in Week 10. In Week 16, he collected a season-high eight combined tackles during a 24-12 loss at the New England Patriots. He finished his rookie season in 2018 with 37 combined tackles and three pass deflections in seven games and seven starts. Wallace received an overall grade of 83.5 from Pro Football Focus, which ranked fifth among all qualifying cornerbacks in 2018. He also received the highest grade among all rookie cornerbacks.
2019 season
Wallace was named a starting cornerback to begin the season, opposite Tre'Davious White. Following an inconsistent start to the season, Wallace eventually saw his playing time reduced in favor of Kevin Johnson. In week 15, Wallace caught his first career interception against the Pittsburgh Steelers on Sunday Night Football, picking off Devlin Hodges to seal a 17–10 Bills victory in the final moments to help Buffalo clinch a playoff berth. In the regular season finale against the New York Jets, Wallace logged another interception off Sam Darnold, but suffered a sprained ankle on the play, which kept him out of the Bills' playoff game against the Houston Texans.
2020 season
On April 2, 2020, Wallace was re-signed to a one-year contract by the Bills.
