Among his family were two sisters and his father, an Air Force fighter pilot, and mother, an English teacher.
[1] Snyder asked Johnstad to assist him with his film 300, a fictionalized graphic novel adaptation of Frank Miller's comic involving the Battle of Thermopylae.
[2] In 2011, Johnstad was working with Snyder to co-write the film The Last Photograph and 300: The Battle of Artemisia for Warner Bros.[1] Johnstad also worked outside of collaborations with Snyder, and was hired by producers Basil Iwanyk and Jason Netter to adapt Max Allan Collins’ novel Black Hats.
[3] In 2015, Variety described Johnstad as beginning "to make a name for himself as writer who delivers big action in his scripts, along with classic heroes audiences love to root for.
[5] Films Johnstad has been assigned to write screenplays for include The Lost Legion for Warner Bros. and Dan Lin, and Aquaman where another script was concurrently in development, by Will Beall.