The North Shore City Council has signed a deal to secure just more than 38 hectares of land in Long Bay.
The agreement with developer Todd Property still needs the approval of the Auckland Transition Agency.
The Long Bay Okura Great Park Society has campaigned for the land to be bought for more than a decade.
Mayor Andrew Williams says the deal will create a legacy for Auckland and a buffer for the Long Bay Regional Park.
He says ratepayers will not have to foot the bill.