Saili was born in Auckland and educated at St Peter's College where he played rugby in the school First XV. He represented New Zealand in schoolboy and global under-age tournaments. After leaving school he played for Auckland Marist. He is the older brother of Blues and All Black centre Francis Saili.
Saili was a junior All Black in 2007 and 2008. In 2007 he was a member of the team which won the International Rugby Board's junior world championship (Under 19), defeating South Africa in the final (31-7). In 2008 he was a member of the New Zealand team which won the International Rugby Board's junior world championship (the inaugural under-20 tournament), pulling off a crushing 38-3 win (four tries to none) over England in Swansea, Wales.