The tense thriller was named Best Picture, while its filmmaker brothers Joel and Ethan Coen jointly received the Best Director prize.
Star Javier Bardem, 38, (pictured far right) took home the Best Supporting Actor Academy Award and the film's final gong was for Best Adapted Screenplay.
There were no surprises when Daniel Day-Lewis, 50, was named Best Actor for his role as an oil tycoon in There Will Be Blood.
Fellow Brit Tilda Swinton, 47, was named Best Supporting Actress for Michael Clayton.
French actress Marion Cotillard, 32, followed her Bafta success by taking home the Best Actress award for La Vie En Rose.
Other winners at the 80th annual Academy Awards held at the Kodak Theatre in Los Angeles included Ratatouille for Animated Feature Film and The Bourne Ultimatum with a trio of Sound and Editing awards. The star-studded event - an international showdown for some of the best films around - was attended by Helen Mirren, Martin Scorsese, Nicole Kidman and husband Keith Urban, George Clooney and Renee Zellweger.
Full list of winnersBest Motion Picture: No Country For Old Men
Lead Actor: Daniel Day-Lewis, There Will Be Blood
Lead Actress: Marion Cotillard, La Vie En Rose
Supporting Actor: Javier Bardem, No Country For Old Men
Supporting Actress: Tilda Swinton, Michael Clayton
Director: Joel Coen and Ethan Coen, No Country for Old Men
Foreign Language Film: The Counterfeiters, Austria
Adapted Screenplay: Joel Coen and Ethan Coen, No Country for Old Men
Original Screenplay: Diablo Cody, Juno
Animated Feature Film: Ratatouille
Art Direction: Sweeney Todd The Demon Barber Of Fleet Street
Cinematography: There Will Be Blood
Sound Mixing: The Bourne Ultimatum
Sound Editing: The Bourne Ultimatum
Original Score: Atonement, Dario Marianelli
Original Song: Falling Slowly from Once, Glen Hansard and Marketa Irglova
Costume: Elizabeth: The Golden Age
Documentary Feature: Taxi To The Dark Side.
Documentary Short Subject: Freeheld
Film Editing: The Bourne Ultimatum
Make-up: La Vie En Rose
Animated Short Film:Peter & The Wolf
Live Action Short Film: Le Mozart Des Pickpockets
Visual Effects: The Golden Compass