The 50-year-old star was recognized for his role in 'There Will Be Blood' and when he collected the award he knelt before Mirren, who was named last year's Best Actress for her portrayal of Britain's Queen Elizabeth in 'The Queen'.
She then used the golden statue to tap Day-Lewis on each shoulder, mimicking how the monarch uses a sword to award a knighthood.
The British actor joked: "This is the closest I'll ever come to getting a knighthood, so thank you."
He then added: "I hope that all those to whom I owe and feel the deepest gratitude will forgive me if I say just simply, thank you all."
Day-Lewis - who has previously won the Best Actor Oscar for his role in 'My Left Foot: The Story of Christy Brown' - beat off competition from George Clooney, Johnny Depp, Viggo Mortensen and Tommy Lee Jones.
French star Marion Cotillard was named Best Actress for her role in 'La Vie En Rose', beating the hot favorite Julie Christie.
Upon collecting her award, Marion, who looked stunning in a cream dress, thanked the film's director, Olivier Dahan.
She said: "Maestro Olivier, you rocked my life. You have truly rocked my life.
"Thank you life, thank you love. And it is true that there are some angels in this city."
Tilda Swinton won Best Supporting Actress for 'Michael Clayton', and dedicated her award to her co-star George Clooney.
She joked: "Clooney, you know, the seriousness and the dedication to your art, seeing you climb into that rubber batsuit from 'Batman and Robin', the one with the nipples, every morning under your costume, on the set, off the set, hanging upside-down at lunch, you rock, man."
The biggest winner of the night was 'No Country For Old Men', which was named Best Film and Best Adapted Screenplay, while brothers Joel and Ethan Coen were jointly awarded Best Director.
Javier Bardem also won Best Supporting Actor for his role as a hitman in the film.

The Oscar 2008 winners in full:

Best Picture - 'No Country For Old Men'

Best Director - Joel and Ethan Coen, 'No Country For Old Men'

Best Actor - Daniel Day-Lewis, 'There Will Be Blood'

Best Actress - Marion Cotillard, 'La Vie En Rose'

Best Supporting Actress - Tilda Swinton, 'Michael Clayton'

Best Supporting Actor - Javier Bardem, 'No Country For Old Men'

Best Foreign Language Film - 'The Counterfeiters' (Austria)

Best Animated Feature Film - 'Ratatouille'

Best Adapted Screenplay - 'No Country For Old Men'

Best Original Screenplay - 'Juno'

Best Music (score) - 'Atonement'

Best Music (song) - 'Falling Slowly' - 'Once' (performed by Glen Hansard and Marketa Irglova)

Best Documentary Feature - 'Taxi to the Dark Side'

Best Documentary Short Subject - 'Freeheld'

Best Visual Effects - 'The Golden Compass'

Best Cinematography - 'There Will Be Blood'

Best Art Direction - 'Sweeney Todd: The Demon Barber of Fleet Street'

Best Animated Short Film - 'Peter and the Wolf'

Best Short Film - 'Le Mozart des Pickpockets'

Best Costume Design - 'Elizabeth: The Golden Age'

Best Make-up - 'La Vie En Rose'

Best Sound Editing - 'The Bourne Ultimatum'

Best Film Editing - 'The Bourne Ultimatum'