Rachel Stevens and Melanie C will be performing live in Trafalgar Square as London waits to find out the result of the race to host the 2012 Olympic Games and Paralympic Games.
The pop stars will join a host of British Olympians including Athens golden girl Dame Kelly Holmes at the event, which takes place between 12 noon and 2pm on Wednesday 6 July.
Giant video screens will show live coverage of events from Singapore, including the dramatic moment when International Olympic Committee President Jacques Rogge announces which city will host the 2012 Games.
The result from Singapore is expected to come through at approximately 12.45pm British Summer Time.
Former S-Club star and chart-topping solo artist Stevens said: "I'm delighted to be performing in Trafalgar Square on 6 July to support London's bid on such an important day.
"It would be fantastic for this country if the Games were held here."
Capital FM DJs Margherita Taylor and Katy Hill will host the event, which will also feature a live performance of London's bid anthem 'Proud' by Heather Small.
Indian drumming group the Dhol Academy and the Mahogany Carnival Group will also be entertaining the crowd in the run-up to the decision.
A special 'Decision Day' event is also taking place at Stratford - close to the site of London's Olympic Park - where Javelin star Tessa Sanderson and Modern Pentathlete Georgie Harland will be making an appearance.
And delegates at SkillCity - a major careers and training event in London's Docklands - will also be able to watch all the action from Singapore on giant video screens.
London 2012 ambassadors John Amaechi and Alison Mowbray will be at SkillCity, which takes place at ExCeL, another of London's proposed venues for the 2012 Games.
4 July 2005