The two actors, who co-starred in the film Salmon Fishing in the Yemen, will provide their voices for a "five-minute opus magnus" at the start of Friday night's (July 27) ceremony.
"It is pretty breathtaking," executive producer Jim Bell said during a press conference. "I think it will give you a sense of the flavour of our coverage and the feeling we're all having going into these games."
Bell went on to speak about London's opening ceremony, insisting that it will not disappoint.
"Having seen it... I can tell you that it includes some amazing moments, including one that I think will be among the most astonishing and memorable in opening ceremony history, and one that people will be talking about for years to come," he promised.
The opening ceremonies will air from 7.30pm ET on NBC in the US.