A ceremony to mark the 12-month point before the Olympics will be held in Trafalgar Square in central London on Wednesday and screened live on TV.
International Olympic Committee president Jacques Rogge and Mayor Boris Johnson will invite the world's athletes to come to the London Games.
Tom Daley will dive into the pool at the new Olympic Park aquatics centre.
The design of the Olympic medals will be revealed during the 1900 BST (1800 GMT) ceremony, on BBC One in the UK.
"The one-year-to-go mark is London's invitation to the world to come to the Games," said London 2012 chief Lord Coe.
"We share the nation's excitement and we won't let you down," he added.
Teenage British diver Tom Daley will make the first dive at the aquatics centre in Stratford, east London, which will be unveiled on Wednesday.
The gold, silver and bronze medals to be awarded next year will also be revealed to the world.
The event will also give people the chance to see how some major Olympic venues and the city will look during next year's Games as key buildings will be decorated for Games time.
"This ceremony marks the most important milestone to date on the journey to the London Games," said Mr Johnson.
"Our venues are nearly all complete and our preparations to ensure all our visitors can experience the Games wherever they are in the capital are well advanced.
"With a year to go we can safely say we are ready to welcome the world."
The BBC will have comprehensive coverage of the year-to-go celebrations online, on television and on radio.