Nils Allen Stewart Jr. was born in Beverly Hills, California. His father, Nils Allen Stewart, is a professional stuntman. His younger sister, Fivel, is also an actress and recently appeared in the second season of the Netflix original dramedy Atypical. His mother has Japanese, Chinese, & Korean ancestry & his father has Russian, Scottish, & Blackfoot ancestry. Stewart was a former member of T-Squad, a Disney hip-hop/pop group, and performed with his sisters, Fivel and Maegan, as part of "TSC" (The Stewart Clan).