The Everybody Loves Raymond star will appear in the final season's 20th episode, according to The Hollywood Reporter.
Roberts will play a wealthy woman who hires Gabrielle (Eva Longoria) to be her personal shopper.
Carlos (Ricardo Chavira) also wants the character to donate to his new charitable organisation, and he and Gabrielle both end up competing for her attention.
81-year-old Roberts, who played Marie Barone on Everybody Loves Raymond from 1996 to 2005, recently appeared on Grey's Anatomy and The Middle.
She has also signed up for a role in ABC comedy pilot Counter Culture opposite Margo Martindale and Luis Guzman.
Desperate Housewives continues on Sundays at 9/8c on ABC.
> Read Digital Spy's recap of the latest Desperate Housewives episode