Former NRL star-turned commentator Matthew Johns nominated Brennan as the game's next great coach.
"I've had a rap on fellow named Garth Brennan for a long time," Johns said on his Triple M radio show.
"Brennan has been coaching lower grades at Penrith for a number of years now and he's won competition after competition.
Kidwell is pleased to have confirmed his assistants.
"Garth and Brian have the skills and depth of experience to be a very good fit for us. They also share my approach to standards and values - and they are really fizzing to be part of our setup.
"Brian's record speaks for itself. He has played first grade, and coached in the NRL and UK Super League. He also coached NSW Country, so knows what's required to bring players together from their clubs for short campaigns."
"Garth has been talked about for some years, but it's tough for these guys to find a first-grade coaching spot, there is so much competition for places. Despite that, I know he will offer us a lot. He has proven over many years that he can relate to the young players to get the best out of them and I am confident that he will be an asset to our coaching group."
In addition to current selection panel of Kidwell, Tawera Nikau and Tony Iro, the Kiwis have also added Hugh McGahan.
The Kiwis campaign kicks off at Mt Smart Stadium on October 28 when they play Samoa before heading to Christchurch to face Scotland (Nov 4), and Hamilton to take on Tonga (November 11).
There are quarter-finals in Wellington and Christchurch (Nov 18), a semi-final at Mt Smart (November 25) before the tournament final in Brisbane.