Phelps follows quarterback Peyton Manning and basketball star LeBron James, who also have starred on the show, which launches its 34th season Sept. 13. Rapper Lil Wayne, whose most recent album, Tha Carter III, sold more than 1 million copies in its first week, will be the musical guest.
Phelps won gold medals in all eight races in which he participated - some in stirring fashion - this month in Beijing, breaking Mark Spitz' 36-year-old record for the most gold medals won in a single Olympics. Phelps will be the third Olympian to host the show, behind skater Nancy Kerrigan and skier Jonny Moseley.
Since his record-setting performance, Phelps has vaulted into the pop culture mainstream, his love life the source of Internet rumors and his Facebook page flooded with millions of requests.
A day after winning his last gold medal, Phelps attempted to do a promotional appearance for VISA at Prince Jun Palace in Chaoyang Park in Beijing. Before he got halfway to the stage, a sea of about 40 photographers and reporters surged toward him.
Phelps also appeared twice recently on the cover of Sports Illustrated. Financial analysts are predicting sponsorship deals worth as much as $40 million over the next four years.
Acting, though, is a new venture for Phelps, and following up the comedic antics of past athletes on Saturday Night Live might prove difficult.
Manning's faux United Way skits became an Internet sensation, while James' dance routine on the show proved to be a major hit.
Attempts to reach Phelps and his representatives last night were unsuccessful.
Saturday Night Live debuted in October 1975. Cast members of the 90-minute late-night show have included such actors as Chevy Chase, Eddie Murphy, Bill Murray, Martin Short and Billy Crystal.
Show officials could not be reached for comment.