The company declined to comment on the vendor and a spokesman said the selling price would depend on what the buyer wanted to do with it.
"We honestly wouldn't know until the tenders close."
The property package includes 460ha known as Renall's Farm.
It was previously owned by developer Rick Martin's Cornerstone Group, which had plans for 2300 new homes in the area. The development never went ahead and was opposed by locals, including Mr Hart.
He said the area had a long history of early Maori occupation and several pa sites. "I've spent a lot of my own funds opposing that and I've done a lot to preserve a lot of the wetlands and fence off the native bush."
According to the Bayleys website, a previous owner of Renall's Farm applied to the former Rodney District Council in 2006 for a private plan change that would allow the construction of an "urban village with associated countryside living".
"This private plan change has not proceeded, however this land holding reserves outstanding opportunities for the future, as pressure from Auckland's expansion continues in the years to come," the website said.
Mr Hart has represented high-profile killers, including Antonie Dixon, who attacked two women with a samurai sword and shot a man dead in 2003. The barrister is facing four misconduct charges brought by the Standards Committee of the Law Society, including an allegation that he "grossly overcharged" a client in a criminal case and billed him for $35,000 plus GST.
The hearing was postponed last month when Chief High Court Judge Justice Helen Winkelmann said a key witness for the committee had been appointed a District Court judge. It is understood the witness, an experienced criminal defence lawyer, was to give evidence on what would be an acceptable amount to charge a client.
