Campanella's film had already won numerous awards
Argentine drama The Secret in Their Eyes has taken the Academy Award for best foreign language film, giving Argentina its first Oscar since 1985.
It beat favourites The White Ribbon from Germany and France's A Prophet.
"I want to thank the academy for not considering Na'avi a foreign language," joked director Juan Jose Campanella in reference to Avatar's alien language.
The Secret in Their Eyes, set in 1999, tells the story of a man who sets out to solve a murder committed in 1974.
The film, starring Ricardo Darin, Soledad Villamil and Javier Gordino, was Argentina's highest-grossing film in 2009.
The Oscar victory is the first for Argentina since 1985, when The Official Story was voted best foreign language film.
As well as A Prophet and The White Ribbon, other films nominated in the foreign language category this year were Ajami from Israel and Peruvian film The Milk of Sorrow.
The Secret in Their Eyes derives its title from the intentions reflected in the characters' eyes.