Stewart, who presents The Daily Show, fronted the Oscar ceremony in 2006, but received mixed reviews. Ellen Degeneres replaced him for the 2007 awards.
It may be that, with a presidential election due in autumn 2008, organisers want someone at home with politics. The Daily Show makes no secret of its liberal bias - right-wing Fox network even set up its own satirical politics show to run against it - and Stewart's presence will doubtless antagonise conservative commentators.
But the New York comic hinted there could be more on the way. "I'm thrilled to be asked to host the Academy Awards for the second time because, as they say, the third time's a charm," Stewart teased.