Harry, Zayn, Liam, Niall and Louis will perform 'What Makes You Beautiful' from a carnival-like flat-bed truck, moving around the athletics track at Stratford's Olympic Stadium.
An insider told the Daily Mirror newspaper: "It's all hush-hush and the boys have been sworn to secrecy.
"But they've been at rehearsals and can't wait to do their bit. It will be an unforgettable occasion and they feel privileged to be a part of it."
Madness and the Pet Shop Boys have been added to the bill, which also includes George Michael, The Who and the Spice Girls.
The 'Wannabe' singers are expected to perform their debut hit, and have been rehearsing for eight hours a day for the past eight days, ensuring the gig tops Danny Boyle's Opening Ceremony.
Their set is said to be "absolutely ingenious".
It is still not known whether Take That will perform following this week's tragic news that Gary Barlow and wife Dawn's daughter, Poppy, was stillborn.
There was speculation last night that Kate Bush could be making a surprise comeback appearance, too, after a remix of her track 'Running Up That Hill' appeared on Amazon.
The page, which has since been taken down, showed the 2012 reworking available for download to coincide with the August 12 ceremony.
Muse have also confirmed they will be performing.