Matthews was a preseason All-Big Ten selection by the Big Ten Media. Prior to the season he was one of nine Big Ten players named to the preseason John R. Wooden Award watchlist and one of eight named to the preseason Naismith College Player of the Year watchlist. On December 15, Michigan defeated Western Michigan 70–62 with 25 points and 10 rebounds from Matthews, for his fifth career double-double and first of the season. On January 13, Michigan defeated Northwestern to establish a school record for best start at 17–0 and tied the school's record 17-game win streak. On January 22, Michigan defeated Minnesota 59–57 after a buzzer beater by Matthews. On January 25, Matthews posted 10 points and a career-tying 11 rebounds for his sixth career double-double in a 69–46 victory over Indiana. The 23-point victory marked the largest ever by Michigan on the road against Indiana. On February 6, Matthews was the only Big Ten Athlete named a Julius Erving Award Top 10 finalist. On February 9, Michigan defeated (#19/#19) Wisconsin 61–52. Michigan was led by Matthews with a game-high 18 points. The teams each scored 27 in the first half and 16 of Matthews 18 came in the second half, including 14 of Michigan's 19 points in a decisive stretch taking the score from 38–35 to 57–50 with 23.8 seconds remaining. Matthews missed the final three games of the regular season due to an ankle injury. Following the season, he was a 2019 All-Big Ten honorable mention selection (media). On March 21, Matthews posted a game-high 22 points and ten rebounds for his seventh career double-double in a 74–55 victory over Montana in the first round of the 2019 NCAA Tournament. Following the season, on April 9, 2019, Matthews (along with teammates Iggy Brazdeikis and Jordan Poole) declared for the 2019 NBA draft with the intention of hiring agents. On April 17, Matthews announced, via the Michigan basketball Twitter account, that he would forgo his remaining year of eligibility at Michigan.