Clarkson was the first winner of "American Idol" in 2002. Her hits include "A Moment Like This" and "Because of You."
Organizers say she'll perform at Endymion's ball at the Superdome after the parade.
Clarkson may be upstaged at the Feb. 9 parade by a float that organizers say will be the largest and most elaborate in Carnival history.
The super float will be 330 feet long and carry more than 200 riders.
Fat Tuesday translated into French is Mardi Gras and is on Feb. 12 next year. It is traditionally marked with feasting the day before the Catholic season of Lent begins on Ash Wednesday.