Stanfield's first role was in the short film Short Term 12 (2009), which was filmmaker Destin Daniel Cretton's thesis project at San Diego State University, and won the Jury Award for U.S. Short Filmmaking at the 2009 Sundance Film Festival. A year later, he appeared in the short film Gimme Grace (2010), before he gave up acting for several years. He went on to work a number of different jobs—roof work, gardening, at AT&T, and at a legal marijuana dispensary—before he was contacted by Cretton to reappear in a feature-length adaptation of Short Term 12, his first feature film. For the duration of the film's production, Stanfield practiced method acting, distancing himself from the other cast members like his character, Marcus. He was the only actor to appear in both the short and feature films.
Short Term 12 won the Grand Jury Prize for Best Narrative Feature at the 2013 South by Southwest film festival, and Stanfield was nominated for the Independent Spirit Award for Best Supporting Male.
In 2014, Stanfield co-starred in The Purge: Anarchy and Selma, in the latter playing civil rights Activist Jimmie Lee Jackson. He appeared in James Franco's upcoming film Memoria and in Don Cheadle's Miles Ahead. Stanfield also starred in the fantasy horror thriller film King Ripple, by the Michigan filmmaker Luke Jaden, and the music video for the Run the Jewels song "Close Your Eyes (And Count to Fuck)". In 2015, he portrayed Rapper Snoop Dogg in the biopic Straight Outta Compton. In 2017, he acted in Netflix's Adam Wingard's Death Note.
Stanfield has been in a relationship with Actress Xosha Roquemore since at least August 2015 and in March 2017 the couple announced they were expecting their first child together; the baby was born later that June.
In 2016, he appeared in the Oliver Stone biopic Snowden and began starring on the comedy-drama TV series Atlanta. In 2017, he appeared in the critically acclaimed horror film Get Out, and the fantasy-thriller film Death Note, an adaptation of the manga of the same name.
In 2017, he appeared in the critically acclaimed horror Get Out.