The son of former Balmain, NSW and Australian rugby league player Garry Jack,[1] Kieren is the eldest of three brothers raised in the Cherrybrook suburb of Sydney.

[2] Kieren was educated at West Pennant Hills Primary School where he played in its AFL team, including the premiership side in 1999.

His first experience of Australian rules was in the Paul Kelly Cup in 1998 in primary school playing for the junior Pennant Hills Demons AFC.

His career year was capped off with taking home the Bob Skilton Medal as the Swans' best and fairest player over Shane Mumford and Josh Kennedy.

He finished 4th in the 2012 Bob Skilton Medal a week after kicking 2 crucial goals in the Swans' Grand Final victory at the MCG over the Hawthorn Hawks.