He completed his college career for the St. John's Red Storm before playing professionally in Turkey, Israel and Russia.

Harrison attended Dulles High School in Sugar Land, Texas, where he was coached by Mike Carrabine.

As a junior, he posted averages of 20.8 points, 5.2 rebounds, 4.2 assists and 2.2 steals per game, earning Harrison 2009–10 Houston Chronicle Player of the Year and District MVP honors.

[6] In the offseason, he attended a camp led by former NBA player John Lucas aiming to work on anger management issues.

The two drove to practices together and seeing how Rice, who allegedly made homophobic comments to players, worked on his own issues gave Harrison a new perspective on life.

[8] He was selected to the District II (NY, NJ, DE, DC, PA, WV) All-District team by the United States Basketball Writers Association (USBWA).

[16] On January 20, 2018, Harrison recorded a career-high 34 points, shooting 11-of-19 from the field, along with six rebounds, five steals and four assists in a 94–91 win over Maccabi Tel Aviv.

[17] On April 28, 2018, Harrison tied his career-high 34 points, shooting 11-of-18 from the field, along with six rebounds and three assists in a 90–86 win over Hapoel Jerusalem.

Harrison helped Gilboa Galil reach the 2018 Israeli League Playoffs, where they eventually lost to Hapoel Jerusalem.

On July 24, 2018, Harrison signed a two-year deal with the Russian team Enisey of the VTB United League.

[19] On April 24, 2019, Harrison recorded a double-double and a season-high of 34 points and 12 rebounds, shooting 10-of-15 from the field, along with four assists in a 94–86 win over Khimki.