Smith was born in Elmhurst, Illinois. He has a brother Brian.
A Chicago-area hospital worker approached his parents about him auditioning for the leading role in The Mighty, a feature film about a character with Morquio Syndrome. Kieran Culkin was cast instead, but Smith was recommended for the title role of Simon Birch (1998), a film based loosely on John Irving's novel A Prayer for Owen Meany, which also called for a small child actor.
He graduated from York Community High School in Elmhurst in 2005. He has undergone several operations including a spinal fusion and two bilateral osteotomies. He graduated from the Massachusetts Institute of Technology in 2009, and Gallaudet University in 2012. and now works as a software engineer.