"Django Unchained" actors Jamie Foxx and Samuel L. Jackson took home popcorn-shaped trophies for best "WTF moment" for the scene in which Foxx's vengeful slave berates and unleashes a volley of gunshots at Jackson's servile black manservant.
The MTV Movie Awards, one of Hollywood's biggest youth-friendly ceremonies, rewards movie performances from the past year as well as promoting upcoming blockbusters and new music.
Fans will be treated later to the first sneak peek of "The Hunger Games: Catching Fire" ahead of the release in November of the sequel to the young adult hit movie.
Watson, 22, found fame as brainy schoolgirl Hermione Granger in the first "Harry Potter" movie in 2001. She has gone on to make some 15 movies, including lead roles in all eight Potter films.
"I look back at all of the work I have done over the past 14 years and many things come to mind, notably how bad my hair was in the first Harry Potter film!" the British actress joked, accepting her award.
"Becoming yourself is really hard and confusing," she added.
"Django Unchained" and raunchy comedy "Ted" went into Sunday's ceremony with a leading seven nominations apiece, including the top prize, movie of the year.
Winners are chosen by fans and voting for the movie of the year continues throughout the two-hour ceremony broadcast live on MTV around the world from Los Angeles.
The comic book superheroes of "The Avengers" won the best fight category, with popular, tongue-in-cheek awards like best shirtless performance and best villain to be presented later.
Foxx is also being honored on Sunday with the MTV Generation Award, while Will Ferrell won the Comedic Genius Award for his long career on film and television including "Elf," "Saturday Night Live" and "Anchorman."