In 2010, Mannah played for both the City team and the New South Wales State of Origin team as a substitute. In 2011, Mannah played again for City and all three State of Origin games for New South Wales. In the final two games of the series Mannah started both and was actually one of only 2 prop forwards playing for New South Wales after coach, Ricky Stuart opted for a faster, more mobile pack and played second-rowers in the prop forward position. At the end of the 2011 season, Mannah was selected by Julia Gillard to join the Prime Minister's XIII for their annual clash with the PNG Kumuls.