As a relative newcomer to the sport, Horn won his first Australian title in 2009 and repeated the feat in 2011. He went on to win a silver medal at the Gee-Bee Tournament in Helsinki and compete at the 2011 AIBA World Boxing Championships in Baku where he lost to eventual champion Everton Lopes in the second round. In 2012, he picked up his third Australian title and first Oceania title to earn a spot at the London Olympics.