Grant attended DeMatha Catholic High School in Hyattsville, Maryland, where as a senior in 2011–12, he averaged 12.5 points in 23 games.

[12] On November 1, 2016, Grant was traded to the Oklahoma City Thunder in exchange for Ersan İlyasova and a protected draft pick.

[13] He made his debut for the Thunder the following day in an 85–83 win over the Los Angeles Clippers, recording six points, two rebounds, and two blocks in 18 minutes off the bench.

[24] On September 15, 2020, in a Game 7 win against the favored Clippers, Grant outscored Paul George 14 to 10 while playing 9 fewer minutes.

However, he struggled against LeBron James and Anthony Davis in the Western Conference Finals, as the Nuggets fell to the Los Angeles Lakers in five games.

On November 22, 2020, Grant signed a three-year, $60 million contract with the Detroit Pistons through a sign-and-trade with the Denver Nuggets.

Detroit also received draft rights to 2015 second-round pick Nikola Radičević in exchange for cash considerations.

[28][29] Grant ended the season as a Most Improved Player award finalist, finishing second behind Julius Randle, while averaging a career high in points per game.

[31] On December 16, he underwent surgery to repair the ulnar collateral ligament (UCL) in his right thumb and was ruled out for at least six weeks.

Grant's uncle, Horace (twin brother of Harvey), played college basketball at Clemson and was a four-time NBA champion with the Chicago Bulls and Los Angeles Lakers.