He played college basketball for the Tennessee Volunteers, earning first-team all-conference honors in the Southeastern Conference (SEC) as a senior in 2015.

He was selected in the second round of the 2015 NBA draft by the Heat and has also played for the Philadelphia 76ers, Dallas Mavericks, Boston Celtics, San Antonio Spurs, and New Orleans Pelicans.

[4] He failed to appear in the Heat's first four games of the season before making his NBA debut on November 5 against the Minnesota Timberwolves, playing in just under seven minutes of action.

[5] On November 12, in just his third NBA game, Richardson started at shooting guard in place of the absent Dwyane Wade.

[10] On February 24, he recorded his first double-digit game in the NBA, scoring 15 points on 5-of-6 shooting off the bench in a 118–111 loss to the Golden State Warriors.

[15][non-primary source needed] On December 27, 2016, he tied a career high with 22 points in a 106–94 loss to the Oklahoma City Thunder.

[28] On November 18, 2020, Richardson, along with the draft rights to Tyler Bey, were traded to the Dallas Mavericks in exchange for Seth Curry.

[30] On July 31, 2021, Richardson was acquired by the Boston Celtics using the remainder of the Gordon Hayward traded player exception in exchange for young center Moses Brown.

On February 10, 2022, Richardson was traded along with Romeo Langford to the San Antonio Spurs in exchange for Derrick White.

[34] On February 9, 2023, Richardson was traded to the New Orleans Pelicans in exchange for Devonte' Graham and four future second-round picks.