Auckland Council is paying $60.7 million for Auckland University's home for cricket and rugby.
Colin Maiden Park in St Johns adds 20ha to the public's sporting fields portfolio.
In March, the Herald reported the university was giving the council first option to buy as it planned to quit its Tamaki campus in favour of consolidating in the city core, Grafton and Newmarket.
Yesterday, Mayor Len Brown announced an unconditional agreement, saying it was one of the most significant urban park acquisitions in Auckland's history.
But the purchase was an unbudgeted item and had to be factored into the 2014-15 draft annual plan to be finalised next year.
Three parcels of land around Colin Maiden Park might be sold to recover some of the cost.
Vice-chancellor Stuart McCutcheon said the university opened the sports complex in 1978. But it was not in the business of owning and running parks and about 90 per cent of the users were not students.
He said the deal with the council was negotiated over five months and came to a sensible conclusion.
"Our clubs remain on the park; the city wins because it gets a new university campus which will bring big economic benefit and gets a 20ha recreation facility.
He would not comment on whether the $60.7 million price was the going rate - driven by interest from residential developers.
Three years ago, the council paid $10.3 million for the 4.4ha Liston Park in Ellerslie to help ease a shortage of sports fields.
Councillor Christine Fletcher said the purchase "creates an incredible 44ha sports and open space complex for Auckland".