Lord Moynihan is stepping down as chairman of the British Olympic Association (BOA).
Lord Moynihan, who helped steer Team GB to 29 golds and third place in the medal table at the London 2012 Olympics, has written to the the BOA executive board, the National Olympic Committee and the BOA advisory board to confirm his decision.
He intends to stay on as chairman until an election is held in November to find a successor.
He revealed that his priorities include a smooth handover to his successor and ensuring there is a strong sports policy so the momentum from the Games is not lost.
In his letter, Lord Moynihan wrote: "Firstly, I want to congratulate you all on a magnificent Olympic Games and to thank you for all that you have done to ensure their success.
"The last two weeks have united and inspired the whole country and have surpassed all expectations.
"I am enormously proud to be able to say that with your help, Team GB has not only succeeded at London 2012, it has excelled.
"The years of hard work and preparation undertaken by everyone at the BOA have paid historic dividends through the delivery of so many outstanding personal bests by our athletes.
"After their incredible performances, securing an historic third place for Team GB in the medal table, the 541 athletes of Team GB truly deserve to be called our 'greatest team ever'.
"The Prime Minister's announcement that funding for our Olympic athletes is now guaranteed for the next four years in the run-up to Rio represents the successful culmination of our campaign for secured lottery funding.
"It means that our athletes' success in Beijing 2008, now built on and furthered during London 2012, can be carried forward with renewed confidence in Rio 2016.
"As a result of the success of Team GB, the reputation of the BOA, its staff and volunteers is rightly at an all-time high. We now have a unique opportunity to capitalise on this success and to build a stronger and even more victorious team in the future.
"Over the last seven years, the BOA has striven to become a modern, accountable, performance-driven, highly professional, athlete-centric organisation, of which we can all be extremely proud. On a year-by year basis, the athletes have been increasingly supportive of the backing they have received from the BOA performance teams in the Olympic villages and at the venues.
"Put simply: this was a job outstandingly well done by everyone who works at the BOA, the governing bodies and the volunteers who joined the BOA team in the run-up to the Games and I am exceptionally grateful to you all."
In leaving the BOA, Lord Moynihan feels he will be free to push for a coherent sports policy in the House of Lords without ties to a major sports body.
He leaves a year before the end of his second four-year term, having overseen an overhaul of the BOA aimed at preparing for London 2012.
Candidates to succeed him could include Richard Laman, president of GB Hockey and a BOA board member, and BOA deputy chairman David Hemery.