Horner was born in Brisbane, Queensland, Australia on 24 January 1983. He discovered that he loves acting after appearing in school productions. Along with acting, Horner's talents include playing the guitar and writing music. He enjoys the outdoors and playing football (soccer), volleyball, tennis, swimming, skiing, snowboarding, and kayaking.
Horner attened St. Peter's Lutheran College in Indooroopilly, Brisbane, Australia. He pursued acting after he had graduated. Since 2001, he has appeared in various TV programs.