He would continue international responsibilities as chair of the Business and Industry Advisory Committee to the OECD and member of the governing body of the International Labour Organisation until the end of those terms in mid-2017.
He would help BusinessNZ in their search for a new chief executive.
"Over the next few months I will look forward to discussing future business and career options with a variety of people. I have no concrete plans for what might happen next, although I will investigate taking on a small number of directorships and engaging in consulting work in New Zealand and internationally."
He said a decade was long enough in the job which he had enjoyed every day of.
"I will remain based in New Zealand and look forward to continuing contributing to New Zealand's success in some different way in the future."
BusinessNZ president Laurie Margrain said O'Reilly had given outstanding service to the business and wider community and the organisation was sorry to lose his contribution.
"This is a challenging role requiring enormous commitment on behalf of the business community and a high degree of involvement with central and local Government," she said.
"We do, in every sense, wish him well in future endeavours and feel sure that there will remain significant areas of business policy where a degree of future association will be beneficial," Margrain said.
The search for a successor for O'Reilly will begin immediately.