Bromwich of Māori descent played junior rugby league for the Manurewa Marlins. All of his junior career was spent in Auckland, being an Auckland Sea lions NJC under 18s grand finalist and Auckland Rugby League under 18s grand finalist in 2006, playing with the Auckland Metro under 18s in 2007 and playing for the Auckland Māori in both 2007 and 2008. In 2007 he played representative football for the New Zealand Māori under 18’s side. He moved with his family to Australia in his late teens and played for the New South Wales country club Orange Hawks in 2008. His good form in the 2008 season was acknowledged when he became a New South Wales Country Rugby LeagueGroup 10 under 23’s representative player.
Bromwich signed with Melbourne in 2009. In his first season with the club he was voted Toyota Cup NYC under 20sprop forward of the year and was named in the NYC team of the year after Melbourne won the competition. Bromwich played in the Storm's under-20s 24-22 grand final win over the West Tigers.