It was Hungarian-French director LÃ¡szlÃ³ Nemes first full-length film and had been seen as the Oscar favorite after winning a Golden Globe and taking the second-highest prize at the Cannes Film Festival.
"Even in the darkest hours of mankind, there might be a voice within us that allows us to remain human," Nemes said on stage. "Thats the hope of this film."
The films title character is an inmate at the Auschwitz concentration camp who risks his life to attempt a proper Jewish burial for a boy he believes is his son.
Hungarian-born Nemes, 39, comes from a family that lost relatives in the Holocaust. The director has said he felt the immediacy and visceral nature of "Son of Saul" was necessary in an age when many people, especially younger generations, see the Holocaust as something from the distant past.
Nemes focused the film on Saul with a continuous series of close shots as he carries out his nightmarish job of herding detainees to their deaths and collecting their bodies for the crematorium, all the while trying to find a way to bury the boy.
Several different languages are spoken in the Hungarian-produced film, reflecting the polyglot nature of the grim world of the World War Two death camps, Reuters reported.
Nemes parents were opponents of the Communist government that ruled Hungary when he was a child, and he spent his teenage years in France. After studying cinema in Paris, he returned to his native land to begin working in filmmaking.
"Son of Saul" marked Hungarys second Academy Award win in the foreign language category after eight previous nominations.