Harrison was initially hesitant to participate in Roots, in part because it would be his fourth portrayal of a slave, and he did not have fond memories of watching the original as a child.

[15] In Reinaldo Marcus Green's Monsters and Men, he portrays Zyrick, a gifted teenage baseball player that becomes politically awakened after seeing a video of a man murdered by the police.

In Sam Levinson's Assassination Nation he has a smaller role as Mason, a friend of the female protagonists and in Anthony Mandler's Monster, based on the Walter Dean Myers novel of the same name,[16] Harrison plays Steve Harmon, a seventeen-year-old honour student whose world comes crashing down around him when he is charged with felony murder.

For his titular role in Julius Onah's Luce alongside Octavia Spencer and Tim Roth, Harrison received critical acclaim as the all-star high school athlete and accomplished public speaker born in war-torn Eritrea adopted in the United States.

Justin Chang of the Los Angeles Times wrote, "Harrison's performance, at once slippery and surgically precise, compounds that ambiguity in ingenious fashion.

[26] Harrison's major breakthrough of the year came with Waves, which premiered to critical acclaim at the Telluride Film Festival on August 30, 2019 and found him reuniting with It Comes at Night writer & director Trey Edward Shults.

[27] In the film, Harrison plays Tyler Williams, a popular high school senior and competitive wrestler whose life goes into disarray after suffering a career-ending injury.

[32] He capped off the year with a supporting performance as musician Teddy Greene in the first season of Epix's Godfather of Harlem alongside Forest Whitaker.

To prepare for the film and its soundtrack, Harrison worked with a vocal coach for 45 minutes a day, to expand his range, and took guitar lessons.

[36] He ended the year with a portrayal of revolutionary socialist Fred Hampton in Aaron Sorkin's biographical ensemble courtroom drama The Trial of the Chicago 7,[37] It was released in selected theaters on September 25, 2020, and began streaming digitally on Netflix on October 16.

[41] Harrison was slated to appear in the second season of HBO's Euphoria, which would have reunited him with Assassination Nation director Sam Levinson,[42] but dropped out due to conflicting schedules attributed to the COVID-19 pandemic.

[46] Upcoming projects In January 2022, it was reported that Harrison will portray the artist Jean-Michel Basquiat in Samo Lives, a biopic that will reunite him with Luce director Julius Onah.