Born in Cherkasy, Ukraine, Mykhailiuk's mother, Inna, is a high school biology teacher, and his father, Iurri, is a college history professor.

[4] He scored 11 points while playing 32 minutes in the Orlando Classic Championship game against Michigan State on November 30, 2014.

On December 22, 2016, in a game against UNLV, Mykhailiuk scored 20 points with 6 rebounds, 2 assists, and 2 steals, helping KU to a 71–53 win.

[10] On April 12, 2017, Mykhailiuk decided to enter the 2017 NBA draft, but did not hire an agent, allowing him to return for his senior year.

[16][17] On February 6, 2019, Mykhailiuk was traded to the Detroit Pistons, along with a future second-round draft pick, in exchange for Reggie Bullock.

[18] On March 13, 2021, Mykhailiuk was traded to the Oklahoma City Thunder, along with a 2027 second-round draft pick, in exchange for Hamidou Diallo.

[20] On February 8, 2023, the Knicks reached an agreement to trade Mykhailiuk, Ryan Arcidiacono, Cam Reddish, and draft considerations to the Portland Trail Blazers for Josh Hart.

[22] He made his Hornets debut on February 15, recording 12 points and two rebounds in a 120–110 win over the San Antonio Spurs.

[24][25] On June 6, 2024, he made his debut in the NBA Finals against Dallas Mavericks, becoming the second Ukrainian to achieve this feat following Slava Medvedenko.

He was selected to the All-Tournament Team,[29] after completing an outstanding championship, averaging 25.2 points, 8.0 rebounds and 3.4 assists per game.

[34] He played for the Ukrainian under-20 team again in the 2017 FIBA Europe Under-20 Championship, where he was the leading scorer of the tournament, averaging 20.4 points per game.