Shadow Olympics minister Tessa Jowell is quitting frontline politics after two decades in Labour's top team, she has announced.
The Labour MP was instrumental in securing and delivering the London 2012 Games while in government and continued to play a key role in opposition.
Labour leader Ed Miliband said the Olympics and Paralympics would not have been possible without Dame Tessa's determination.
Dame Tessa said it was a privilege to have been involved in the London games from start to finish and praised Olympians, Paralympians and the volunteers who helped the spectacular events to run smoothly.
She said: "It has been the greatest privilege to have served as part of Labour's frontbench team, in government and most recently in the shadow cabinet for nearly 20 years.
"To have been able to be part of planning and delivering the Olympic and Paralympic Games from start to finish is a rare opportunity in public life and that too has been a privilege. After 10 years with the Olympics and Paralympics, it is job done.
"I hope people across our country know that the Labour Party under Ed Miliband's leadership wants to speak for them, cares about them and is ready to serve them. Our country has changed this summer and for the better because of the power of the British people, the Games Makers and our great Olympic and Paralympic athletes."
Mr Miliband said Dame Tessa has left an "enormous" legacy and the country owes her a "debt of gratitude". He said: "Over her career, Tessa has been an amazing asset to the Labour Party and to Britain.
"Her legacy is enormous. What we have seen at London 2012 would not have been possible without Tessa's determination and dedication, both in championing the bid and playing a major role in delivering the Games. For this, the whole country owes her a huge debt of gratitude.
"She served in several roles, both in government and opposition, with dedication. Her perseverance played a key role in improving the lives of millions of children by introducing affordable childcare and Sure Start. Tessa will be missed from the shadow cabinet, but I know from her dedication to public service that she has much more to contribute in the future."