The screening also saw the arrival of superstars Brad Pitt and Angelina Jolie, who played the difficult role of Mariane.
Winterbottom's beautifully understated movie, which also stars Daniel Futterman as Daniel Pearl and is co-produced by Pitt, is an up-close, condensed account of Mariane's ordeal. The film, however, was shown out of competition.
It also depicts the intense efforts to find her husband and his eventual beheading at the hands of his captors. The gruesome, shocking video was later flashed worldwide across the Internet.
On Jan 23, 2002, Mariane - who was six months pregnant at the time - was plunged into a forever-changed world when Daniel, who was researching a story on radical Muslim groups for the Wall Street Journal, disappeared.
Speaking to reporters after Monday's screening, Mariane, who is a French national, said she had asked Jolie to play her in the movie after a first meeting with Pitt.
"I felt a great responsibility to Mariane," Jolie said, adding: "I had read her book and I admired her. I was very nervous trying to get her voice in the film right."
Jolie, who was pregnant when she accepted the role, said: "I could not imagine being alone in such a situation." Motherhood had formed a bond between them. The dignity shown by Mariane during the ordeal and since then had been stunning.
Pitt said: "I have great respect and admiration for the story and for Mariane. She had every reason to be embittered. The way she came out of it was incredible."
Shortly after her husband's death became known in 2002, Marian gave a televised interview. Her interviewer asked if she had seen the footage of her husband's decapitation. She replied: "How dare you ask me that?"
Five years later, that same journalist at Monday's press conference in Cannes asked: "Could you please forgive me now?"
Stressing the role of journalists, their credibility, and how Daniel Pearl had mistakenly been perceived as a CIA agent by terrorists should perhaps prompt reflection within the profession.
As he was the first journalist targeted in such a visible manner, and refusing to comment on other cases of abduction, Mariane said journalists should ask: "Is there another way?"
Pitt said the movie's underlying message was of "journalism, interconnections and fighting hatred," and stressed: "The kidnapping did the exact opposite of what it was intended to do because it brought people of every different faiths together."
In the wake of her husband's kidnapping, Mariane's house in Karachi had been transformed into a place in which religion had no role, and everyone involved in the intense search had been united and guided by their concern and desire to find him.