Olympic Delivery Authority chief executive David Higgins has announced he will leave the body in February to take up a position at the helm of Network Rail.
ODA finance director Dennis Hone will replace Mr Higgins as the body works to complete the project to prepare the venues for the 2012 London Games.
Current Network Rail chief executive Iain Coucher announced in June that he would be leaving the rail infrastructure operating body.
ODA chairman John Armitt said:“David has done an inspirational job over the last five years. We have been tasked with delivering the biggest construction project in Europe on a highly contaminated site to the ultimate fixed deadline.
“David set up the ODA from scratch and leaves it with the project on time, within budget and on the verge of completing the first major venues on the Olympic Park. He has done all this at the same time as helping achieve a first class safety record and driving forward innovation in terms of sustainable construction. This is an exciting opportunity for David and I am sure he will do a brilliant job leading Network Rail over the years to come.
“Dennis Hone, who replaces him, has been director of finance at the ODA for the last four years. He has played a key role in our success to date and is a first class replacement. He will give the ODA important continuity as we face the challenges that lie ahead.”