Tim Byles is stepping down as chief executive of Partnerships for Schools.
Mr Byles has been at the helm of the schools capital delivery body for four years.
It is understood he is leaving to establish his own company developing public sector buildings.
PfS had been backed by contractors to play a key role in the new schools system outlined by the James Review last month.
Despite initial problems with Building Schools for the Future, which was scrapped by the coalition government last July, many contractors felt PfS had proved itself as a knowledgable and approachable client.
It is not yet clear who will replace Mr Byles, or what role PfS will have in the new system.
Mr Byles said: “I have always believed in the value of delivering public services using the disciplines of the private sector and I look forward to developing that principle in my next venture, that will bring together the very best of the private, public and third sectors in a new breed of social investment company.
“Meanwhile I believe that the secretary of state and his departmental colleagues will deliver an exciting and much-needed programme of free schools and new academies.“
Michael Grabiner, chairman of the PfS Board said: “Tim Byles has made an outstanding contribution to the delivery of education capital investment in this country, establishing a track record as someone whose core focus is to get the job done.
“Over the past five years, he has impressed me and the PfS Board with his ability to delivery very challenging tasks in a complex and demanding environment. Tim has shown himself to be an individual of the highest integrity and both I and the board wish him every success in the future.”