Cowell is the brutally frank judge on Fox's hit entertainment show "American Idol." Before gaining fame for telling contestants how terribly they they sing, Cowell was a record producer and music executive.
Jackson will be making her first appearance as host of "SNL." She was a musical guest in 1994.
She joins a select list of performers who have been both host and musical guest on the same episode of "SNL" -- including Garth Brooks, Ray Charles, Jennifer Lopez, Dolly Parton, The Rolling Stones, Paul Simon, Britney Spears, Sting, Justin Timberlake and Stevie Wonder.
Jackson is promoting the release of her new CD, "Damita Jo." She made headlines in February after baring a breast at the end of her half-time performance at the Super Bowl in Houston.