David Onions said management duties at the luxury accommodation and golf resort would continue with Gota Ishii as managing director.
"I have very much enjoyed working at Millbrook Resort ... and am inordinately proud of what has been achieved here," Mr Onions said in a statement.
"I'm looking forward now to stepping back from day-to-day operations to be involved at a more strategic level."
Mr Onions will remain in Queenstown to continue his Millbrook duties and also to pursue community and other goals.
He joins Mr Eiichi Ishii, as chairman, and managing director Gota Ishii on the board of Millbrook Country Club Ltd.
Mr Ishii thanked Mr Onions for his contribution and welcomed him to the board.
"We are very pleased to welcome [him] to this non-executive position and look forward to employing his skills at a more strategic level.
"It is very much business as usual at Millbrook with no changes planned to our daily operations."
