Born in Pembrokeshire, Wales, Hamilton came through the academy at the Scarlets before moving to the Cardiff Blues, making his professional debut for the club in the 2010–11 season against Exeter in the Anglo-Welsh Cup. In April 2012 he was named in the Wales Under-20 squad for the Junior World Cup in South Africa. At the competition he played alongside future Wales internationals Rob Evans, Samson Lee and Ellis Jenkins and was part of the starting Wales XV that defeated New Zealand, the first team ever to beat New Zealand at U20 level.