Rivers, 73, and her daughter, Melissa, 37, launched TV Guide Channel's red-carpet programming in January 2005. They had previously appeared as red-carpet hosts on E! Entertainment.
"TV Guide Channel is very appreciative of Joan and Melissa Rivers' contributions to the success of our red-carpet programming over the past three years," Ryan O'Hara, president of TV Guide Channel, said in a statement. "We wish them the best in their future endeavors."
Rinna, 43, recently appeared on ABC's "Dancing With the Stars." She starred on "Melrose Place" and "Days of Our Lives."
"Lisa has the perfect mix of charisma, poise and experience to lead our live red-carpet coverage at the major industry award shows," O'Hara said. "In addition to being an established TV star, she also has fashion expertise as both a business person and commentator, so she is a great fit for this role and for our brand."
Rivers, meanwhile, is staying mum.
"I will tell you my true feelings and experiences as soon as we finalize our new deal," she said in a statement released by her spokeswoman, Judy Katz.
Katz didn't provide further details.