Allison, a dual premiership player with the Kangaroos, has been in charge of the club's forward line since 2010.
North GM football operations Jon Haines says Allison leaves with the Roos' blessings.
"Brett has been outstanding in his role with us over the past four years and departs with the highest amount of respect and good will.
"He will be a great loss and we wish him all the best."
