Blair was born in Alexandria, Virginia and began working with his childhood friend Jeremy Saulnier in 2007 on the film Murder Party. In 2013, he played Dwight Evans in the critically acclaimed film Blue Ruin. In 2015, he starred in Saulnier's film Green Room.
Blair co-wrote the dark comedy Small Crimes starring Nikolaj Coster-Waldau. Blair made his directorial debut on I Don't Feel At Home in This World Anymore. It had its world premiere at the 2017 Sundance Film Festival and won that festival's Grand Jury Prize. It was released on February 24, 2017, by Netflix.
