Allison has spent nine years as a development coach for the Swans, and has recently coached the Swans reserves team to three premiership wins in the AFL Canberra league.
The 41 year-old said he was "extremely excited" about the new role, which will see him take charge of North's backline.
"I wish everyone at the Swans all the best in the future and thoroughly enjoyed my time at the Club," Allison said.
"Paul Roos and the entire team have built a brilliant organisation which I'm sure will continue to be successful."
Swans Chief Executive Andrew Ireland said Allison will be missed by everyone at the Club.
"We thank Brett for his great service over the time he's been with us," he said.
"He has had a really important role in the development of a lot of our young players, and has been a strong contributor to the Club over the past nine years.
"We wish him all the best in what is a great opportunity for him."
