In 2010, Stewart began his career with his role as Kevin Kingston in the TBS sitcom Are We There Yet?. In March 2011, Coy won the Young Artists Award for Best Supporting Young Actor in a Comedy or Drama for his role as Kevin in Are We There Yet?. In 2011, he appeared in 12 episodes of the PBS series The Electric Company, playing Marcus Barnes. In January 2012, Coy’s father, Derek Stewart, published a non-fiction book titled The Unlikely Journey that chronicles Coy’s journey into the entertainment business.

He played the role of Troy Dixon in the Nickelodeon series Bella and the Bulldogs. He starred as Xavier in the 2016 comedy horror web series WTH: Welcome to Howler. In August 2017, Coy Stewart played the primary role in the music video and short film of the song “1-800-273-8255” by rapper Logic which deals with the issues of homosexuality and suicide. In November 2017, it was announced that Stewart had been cast in Agents of S.H.I.E.L.D. as a young Inhuman called Flint. In late 2018, Stewart was cast in a recurring role on the Netflix sitcom Mr. Iglesias.