Mathias is the son of Dan Mathias and has two older brothers. Mathias was a star basketball player at Elida High School. He entered the starting lineup as a freshman and scored over 1,000 points and broke the school scoring record. Mathias scored 28 points a game as a senior at Elida. He committed to Purdue in November 2013.
College career
Prior to Mathias's freshman season at Purdue, he suffered from mononucleosis and threw up before every practice. By the time his health was better, he suffered injuries to both ankles. Despite this, he never missed any games as a freshman but was not at full strength. He averaged 4.8 points and 2.1 rebounds per game as a freshman but shot just 32.2 percent from 3-point range. He had a procedure to correct sinus issues and a deviated septum prior to his second year. As a junior, Mathias averaged 9.7 points a game, led the team in three-pointers and started every game. He developed a reputation as a coach on the floor, with players frequently going to him if they did not understand something basketball-related. He was an All-Big Ten Honorable Mention and was named to the conference Defensive Team. As a senior, Mathias evolved into one of the best defensive players in the Big Ten Conference. He scored 23 points against Fairfield on November 29, 2017. In the Round of 32 of the NCAA Tournament, he hit the critical 3-pointer with 13 seconds remaining that decided Purdue's 76–73 victory over Butler. As a senior, he averaged 12.0 points, 4.1 rebounds and 3.9 assists per game on a 30–7 squad. Mathias finished sixth in the NCAA in 3-point field goal percentage at 46.6 percent and owns the Purdue record for career 3-pointers with 250. He was again an All-Big Ten Honorable Mention and named to the conference Defensive Team.
Professional career
After going undrafted in the 2018 NBA draft, Mathias signed a partially guaranteed contract with the Cleveland Cavaliers, joining the team for Summer League. On August 1, 2018, he signed with Divina Seguros Joventut of the Liga ACB in Spain. After an ankle injury that sidelined him between October and December, some pain remained which prevented him from playing regularly, and on March 3, 2019, he and the club agreed to cancel their contract. On July 26, 2019, Mathias signed a training camp contract with the Dallas Mavericks. He was waived on October 16, 2019, but later added to the roster of the Mavs’ NBA G League affiliate, the Texas Legends. He scored 30 points in a win over Sioux Falls Skyforce on November 27. Mathias scored 30 points in a victory over the Oklahoma City Blue on December 9. Mathias averaged 18.1 points, 4.7 rebounds, 3 assists and a steal per game.
International career
Mathias was a part of the Purdue team chosen to represent the United States in the 2017 Summer Universiade in Taipai, Taiwan. The U.S. received a silver medal after losing in the title game to Lithuania.
