As a sophomore at Kansas, he was a second team All Big 12 selection. He averaged 12.6 points, 3.9 rebounds, and 3.9 assists per game as a sophomore, an increase from the 5.5 points, 1.3 rebounds, and 2.1 assists per game he averaged as a freshman. During his junior season, Mason averaged 12.9 points and 4.6 assists and was named to the Big 12 All-Defensive Team. During his senior season, Mason took on more of a leadership role on the Kansas team, becoming the first player in Big 12 history to average 20 points and 5 assists a game during the regular season. His regular season culminated in receiving multiple awards. He was unanimously selected as the Big 12 Player of the Year, averaging 20.5 points and 5.1 assists in the regular season. He was also consensus first team All-American selection, the NCAA-leading 29th first-team selection in Kansas basketball history. He was awarded multiple player of the year awards including AP Player of the Year, Sporting News Player of the Year, USA Today Player of the Year, Oscar Robertson Award, Naismith Award, and NABC Player of the Year.
Mason was drafted by the Sacramento Kings with the 34th pick in the 2017 NBA draft. He played in the NBA Summer League for the Kings, where he scored 24 points in 24 minutes against the Los Angeles Lakers on July 10, 2017, adding 6 assists, 5 rebounds and 2 steals. For the full 2017–18 regular NBA season, Mason averaged 7.9 points, 2.5 rebounds and 2.8 assists in 52 games. Mason was waived by the Kings on July 4, 2019.
Milwaukee Bucks/Wisconsin Herd (2019–present)
Mason signed a two-way contract with the Milwaukee Bucks on July 26, 2019. In the deal he will split time between the Bucks and their NBA G League affiliate, the Wisconsin Herd. In the G League, he scored 44 points in a win over the Grand Rapids Drive on February 19, 2020. Mason was awarded the NBA G League MVP for the 2019-20 season on June 25, 2020. He averaged 26.4 points, 5.0 assists and 3.4 rebounds per game with the Herd.
Mason and the Kansas Jayhawks competed on behalf of the United States in the 2015 World University Games. He scored 18 points in a double-overtime victory over Germany in the gold medal game and received the Finals MVP award.
Personal life
His father is Frank Mason Jr. and his mother is Sharon Harrison. Mason has 7 brothers and sisters. He grew up in the housing project of Pin Oak Estates located in Petersburg, Virginia, where he developed his game and earned the nickname "The Phenom" by local onlookers within the community. Mason has a son named Amari.