Ferrell, who has been in the Louisiana city since November working on the political comedy "The Campaign," was chosen as the star of Monday's parade, E! News said.
His co-star in the movie, Zach Galifianakis, wore a mask and rode behind Ferrell's float. Ferrell, meanwhile, was wearing a flowing robe and crown, E! said.
"I don't know what to expect. I do have to say, everybody is coming up to me and ... they have the same speech pattern. They go, 'Have you been here before for Mardi Gras?' And I say, 'No.' Then they pause. 'Oh. You're going to have a good time,'" Ferrell told The (New Orleans) Times-Picayune before taking part in the parade. "It's slightly ominous, almost like it's going to be fraternity hazing or something. But I don't know what to expect. I'm not going to try to predict [what happens], and I think it's going to be crazy and fun."