Producers already announced this summer that Clark, who will be making his first television appearance since suffering a stroke last December, will be in Times Square with co-host Ryan Seacrest.
Duff, who has sold more than 1 million copies of her "Most Wanted" CD, takes over a West Coast role that was filled last year by Ashlee Simpson, producers said Monday.
Clark's ABC year-end special, traditionally the party of choice for those who ring in the New Year in front of the television, faces competition from a new Fox show with Regis Philbin. Philbin was Clark's emergency substitute on ABC last year.
Carson Daly will be the host of a New Year's special on NBC.