"I remember watching Entertainment Tonight when it first premiered and dreaming about working for the show someday," O'Dell says. "I am honored to be the one chosen to fill a TV legend's seat and I hope I can do her proud!"
Over the summer, Hart, 60, announced her plans to leave the show in 2011 after nearly 30 years on ET.
"Leaving this job was not an easy decision, but knowing I will pass the baton to Nancy O'Dell makes that decision much easier," Hart said Monday. "Nancy is a talented and respected entertainment correspondent. We have spent many years working on opposite sides of the celebrity battlefield and I know the show will flourish with Nancy as co-anchor."
O'Dell, 44, who served as co-anchor of Access Hollywood for 13 years, will join ET as a special correspondent in January. She'll then take on the role of co-host, alongside Mark Steines, after Hart finishes out her final season on the show.