The 71-year-old was only appointed to the role less than a year ago, and his decision to focus his attentions on Lemley International is likely to leave the organisation reeling.
Lemley, who was previously responsible for delivering the Channel Tunnel, said: 'It has been a privilege to chair the ODA for the last year and lead the organisation through its formative stages.
'The board is now established, along with its separate planning function. The delivery partner has been appointed and the ODA is ready to move to the next stage of its development.
'I am keen to return to the helm of my international construction consulting firm in America, which is increasingly busy with major contracts.'
Olympics Minister Tessa Jowell, who appointed Lemley in November last year, said: 'Jack has done much to help lay the foundations for success for the Olympic construction project over the last year.
'The ODA has made a strong start to its programme. The final site map for the Olympic Park has been published along with the timetable for the construction programme. With the delivery partner on board we now move to the next stage of the project - venue and infrastructure design.
'Jack has played a significant role in getting us to this point and helping ensure the Games and legacy are planned together. I am grateful to him for all he has done and wish him well in the future.'
Roy McNulty, the ODA's deputy chair, has taken over the role as acting chair, alongside chief executive David Higgins, until a decision is made about a permanent successor.