Haneke joins an elite group of two-time winners of the coveted Palme d'Or at the world's biggest film festival after his "The White Ribbon" won in 2009.
The glamorous red carpet awards, held amid thunder, lightning and pouring rain on the French Riviera, brought to an end a 12-day blur of screenings, photo shoots, parties and deal making on Cannes' giant marketplace.
"It's raining a little," deadpanned "The Artist" actor Jean Dujardin, wiping his soaking forehead as he entered the theatre after signing autographs.
Haneke's moving tale set inside a Paris apartment and following a man caring for his ailing wife reduced audiences to tears. The award underlined the 70-year-old's reputation as one of the greatest European directors working today.
"I must say I cried a lot," fashion designer and jury member Jean Paul Gaultier told a news conference.
"I realized that maybe to be on the jury was not so easy because you have to have a lot of emotions sometimes that are strong and make you hurt," said Gaultier, speaking in English. "But I love to be hurt in that way."
Love marked a shift away from Haneke's preoccupation with violence The White Ribbon and 2005's "Hidden".
"The film talks about love," Haneke told a press conference after receiving the Palme d'Or amid loud cheers at the awards ceremony. "Journalists always try to stick a label on directors and say, 'Well, he is a specialist in this or an expert in that.' For a long time, I've been the 'expert' in violence."
Love also won plaudits for its two main actors, Jean-Louis Trintignant and Emmanuelle Riva, both in their 80s.
HOLLYWOOD LEFT EMPTY-HANDED
Brad Pitt, Nicole Kidman, Bill Murray, Bruce Willis, Matthew McConaughey and rising stars Kristen Stewart, Robert Pattinson and Shia LaBeouf all walked the red carpet this year, putting Hollywood at the centre of Cannes.
Yet despite five U.S. pictures appearing in the main competition of 22 films, they all left empty-handed.
Asked about the U.S. productions in competition, and the glamour they brought to the festival, jury president Nanni Moretti said: "I'm not against glamour, but the glamour has to be in films that really please me."
The Grand Prix runner-up prize was awarded to "Reality", Matteo Garrone's examination of society's obsession with celebrity and reality television.
Its central character Luciano was played by Aniello Arena, an Italian serving a lengthy prison sentence who was allowed out of jail on day release to shoot the movie.
Two other previous Palme d'Or winners picked up prizes.
British director Ken Loach won the Jury third prize for his charming Scottish whisky caper "The Angels' Share" and Romania's Cristian Mungiu scooped the screenplay honor for "Beyond the Hills" about a real-life exorcism gone wrong.
His two young stars, Cristina Flutur and Cosmina Stratan, shared the best actress honor, while Danish star Mads Mikkelsen scooped the best actor prize for his portrayal of a man wrongly accused of child abuse in the harrowing drama "The Hunt".
"I'm normally a very cool person but this time I could hardly say anything," said Mikkelsen, who was close to tears as he collected his award.
Mexico's Carlos Reygadas won the best director category for "Post Tenebras Lux", a dreamlike exploration of the undercurrent of menace within Mexican society today.
On the sodden red carpet leading into the Grand Theatre Lumiere, the cast and crew of "Therese Desqueyroux" braved the rain for the world premiere of this year's closing film.
Annie Miller, the wife of the late director Claude Miller who was finishing the film when he died, was in floods of tears as she walked up the stairs and turned to face the ranks of photographers and cameramen.