"Jessica's true vocal talent, unlimited energy and undeniable charisma will truly be a great addition to this year's show," executive producer Carol Donovan said in a statement Thursday.
The People's Choice Awards will be broadcast live Jan. 10 on CBS from the Shrine Auditorium.
Simpson's publicist, Rob Shuter, confirmed her appearance but wouldn't elaborate.
The 25-year-old singer-actress is nominated for favorite song in a movie for her saucy version of "These Boots Are Made for Walkin'" from "The Dukes of Hazzard."
Last month she filed for divorce from former boy band star Nick Lachey, 32. The photogenic pair starred in their own MTV reality show, "Newlyweds: Nick & Jessica."