Rugby is a winter sport, with a long and successful tradition at King's College. Over a third of the male students at school are members of the 15 teams that either compete in the weight-grade or the open-weight competitions, usually with a significant representation in the competition finals.

The popularity of rugby is testament to the school's outstanding success over the years and the school's reputation as one of the leading rugby schools in the Nation. The First XV competes in the highly competitive Auckland Secondary Schools competition, winning the championship as recently as 2005 and being finalists in 2010.