The coalition party's leader made the campaign announcement yesterday afternoon.
The Christ Church Cathedral in the centre of the city was extensively damaged in the February 2011 earthquake.
The about $250 million rebuild project was mothballed in 2024 due to a lack of money.
Further work had got the budget down to about $220 million, but a shortfall of $40 to $45 million remained.
New Zealand First's commitment would meet about a third of that.
"This is a rebuild project that has been waiting for 15 years now and the time has come to ensure this vitally iconic symbol of Christchurch City is completed.
"The city looks at its cathedral as an unresolved problem surrounded by neighbouring solutions. It has been, frankly, left behind.
"There have been a number of plans over the last decade or more to get this done but now there is a board in charge of the rebuild who have the backing of the Anglican Church, local council, key businesses, community leaders and the people of Christchurch.
"This is more than just a church, it is a part of the city's heritage. It is a symbol of the long road of the Christchurch earthquake recovery. Rebuilding the cathedral will catalyse further development around the area and boost important tourism numbers in the city."
The announcement followed a proposal by Christchurch mayor Phil Mauger to use money earmarked for the revamp of Cathedral Square for the restoration of the church itself.
Peters said the project now had an affordable, common-sense plan put forward by Christ Church Cathedral Reinstatement Ltd and about $90 million had already been invested.
"When last in government in 2018 we ensured a government commitment of $25 million towards the project, made up of $10 million with an additional $15 million interest free loan," he said.
"The additional funding commitment from government would see the new, more affordable, and workable project finally get moving. Today, we are making the commitment, that we will give them the tools so they can finish the job."
Peters said he would hold any future coalition partners to this campaign promise.
He said he had not discussed it with his current coalition partners, National and Act.
Christ Church Cathedral Dean Ben Truman was delighted by Peters' announcement.
"The cathedral is such an important part of Christchurch's history and its future, without the cathedral project completed we have a square that is being left behind and that's such a shame when the rest of the city is going so well.
"This kind of leadership from Mr Peters makes such a big difference to confidence to get this project across the line."
The general election will be held on November 7.
