The former Beatle will start the show at 2pm with a version of 'Seargent Pepper's Lonely Hearts Club Band', which may be re-worded to honour the achievements of Bob Geldof.
He will share vocal duties on this opener with U2's Bono and Coldplay's Chris Martin.
They will be wearing multi-coloured military outfits, as worn by The Beatles on the cover of their 1967 album, Seargent Pepper's Lonely Hearts Club Band.
McCartney will close the event eight hours later, with a version of 'The Long And Winding Road'.
At some point during Live 8, Chris Martin will perform a duet with Richard Ashcroft, former lead singer with The Verve.
They will perform a version of Ashcroft's former band's classic single 'Bittersweet Symphony'.
Meanwhile, The Stereophonics are taking a 26 hour detour to be at Live 8.
The band will be playing in Australia tonight, before heading to the UK to play 3 songs at Hyde Park.
Kelly Jones told Radio 1: "We bumped into Bono in a bar in New York and got drunk, and next thing I know, we're doing it. It's not like him telling us to do it, it's just that you start bumping into bands that are doing it, and then you realize it's real."
Snow Patrol will also be heading to Hyde Park having played a major gig the previous night.
The Ulster rockers are playing the Fitzgerald Stadium in Killarney, County Kerry, tonight.
However, the band are unlikely to play more than two songs at Live 8, having been allocated just ten minutes onstage.
Lead singer Gary Lightbody has said that the event's revolving stage will ensure that there are no overruns.
"They just turn you around, even if you are still playing," he explained. "I don't know if they do it to Elton John, but they will certainly do it to us, if we go over."