The performances, featuring artists U2, Coldplay, Madonna, Dave Matthews Band, Jay-Z and Destiny's Child among many others, are being held in eight cities to raise awareness of poverty in Africa.
The telecast is a repeat performance for MTV, which showed the Live Aid concerts two decades ago. Like Live Aid, the Live 8 performances are being organized by Bob Geldof.
America Online, which owns the U.S. rights to the concerts and will beam them on the Internet, is also negotiating with ABC for a prime-time telecast on July 2 following the cable TV coverage.
MTV, VH1 and MTV's college network mtvU will be on the air with the same feed from noon to 8 p.m. EDT that day, switching back and forth from different sites and also presenting packaged reports, like a look back at Live Aid.
Related networks CMT and VH1 Classic will air concert highlights the next day featuring artists geared to their audiences.
It will be the longest period MTV has gone live to cover an event since Woodstock '99, the network said.
XM Satellite Radio will carry the concerts live from Philadelphia, London, Paris, Berlin and Rome, America Online also announced on Wednesday. The Premiere Radio Networks will also carry concert coverage and performances tailored to three different radio formats urban, rock and pop.
Internationally, the MTV, VH1 and Music Factory networks will show hourly bulletins about the show.
MTV, VH1 and CMT, like CBSNews.com, are part of Viacom, Inc.