Cameron intended to reside indefinitely in New Zealand according to his application, and would live at the property, which he would work as a farm.
Cameron joins a growing list of Hollywood heavyweights who call Wairarapa home.
Sir Peter Jackson and Fran Walsh, who together helped create the Lord of the Rings trilogy, live in a multimillion-dollar estate on the edge of Masterton.
Filmmaker, author and artist Vincent Ward owns a home in Greytown.
South Wairarapa farming couple Bill and Annette Shaw struck the deal for the larger Pounui farm overlooking Lake Onoke.
Mr Shaw said confidentiality was a condition of sale.
"I don't have a clue who bought it and what they're going to do with it. I can't discuss it," Mr Shaw said.
He confirmed the purchasing company as Anglin Classics.
Heather and Rob McCreary sold the smaller lot to Anglin Classics in the same deal and Mrs McCreary declined to comment as well.
The latest land deal has stoked political debate and comes only days after the sale of Crafar farms to Chinese interests.
Labour said it approved of Cameron's purchase as long as he intended to stand by his statement to live here indefinitely.
However, NZ First leader Winston Peters said: "To reside in New Zealand indefinitely, well, what does that mean? Full-time, part-time? ... If someone was coming to live in New Zealand and become a New Zealander, that is a different matter."
Mr Peters criticised the decision as typical of the "stupidity" of the Government and the "rubber-stamp merchants" at the OIO.
"If [the applicant] was bringing some expertise to expand this country's export wealth, particularly if it was land to be developed, or better utilised, that would be a different matter.
"But what is the new investment here? It's just a land purchase," said Mr Peters.
Prime Minister John Key said the legislation was "about right", but he would strengthen the law if he thought too much New Zealand land was being sold.
Cameron is expected to start work on the first of two sequels to Avatar later this year.