The 28-year-old's surprise victory, with Italy's Isolde Kostner and Renate Goetschl of Austria in second and third, was a highly emotional affair.
Montillet had never won a medal at a major competition and has only one World Cup victory in her career, a Super-G win last year.
And earlier in the season her national team leader, Regine Cavagnoud, died on a training run in Austria.
Montillet took over the mantle of team-leader and was handed the French flag at the opening ceremony and carried it in memory of Cavagnoud.
7 April 1973
Downhill, giant slalom, super-G
2002 Snowbasin: Downhill: 1st
1998 Nagano, Japan: Downhill 14th
2001 St. Anton, Austria: Downhill: 10th Super-G: 5th
Now the Grenoble-based skier has become the first Frenchwoman to hold the Olympic title.
"It was so wonderful. I don't know if I made mistakes, but I wanted to go fast - I have a lot of emotions," Montillet said after her victory.
"It was very difficult," she added of the four-month period sice Cavagnoud's death.
"As a team we wanted to dedicate the Olympics to Regine.
"I still think of Regine and I will continue to do so. She will always be in my heart and on my mind."
Montillet started 11th, setting a time of one minute 39.56 seconds that proved too much for all her major rivals.
She enjoyed a largely error-free run down the 2,694-metre long course.
However, her early start ensured that she faced a long and anxious wait as the rest of the field took on the Wildflower course.
Having gome down before any of the events big names, it was hard to put her run in perspective.
""I was thinking about her a lot. I
am sure that from where she is she will feel proud of me."
Montillet pays tribute to Cavagnoud
But when Goetschl, 15th out of the start house, failed to match it, it soon became apparent that Montillet could secure the dream result.
World champion Michaela Dorfmeister, Goetschl's team mate, made no impression, finishing outside the top eight.
Germany's Hilde Gerg, the reigning Olympic slalom champion who now concentrates on the speed events after a big crash made the more technical disciplines too painful, finished in fourth.
There was the prospect of an equally emotional finish when Picabo Street, the home favourite, threatened Montillet's time.
Street started strongly in what she later confirmed was her final race before retirement.
However, after matching Montillet's early split times, she tailed off towards the end of the run, ensuring that Montillet enjoyed the fairytale finish and the gold medal.