The 25-year-old world champion made a golden start to her "Vonncouver Games" with the stars and stripes on her ski suit, shrugging off her shin injury to beat team mate Julia Mancuso by a hefty 0.56 seconds.
Austria's Elisabeth Goergl was a distant third, matching the achievement of her mother Traudl Hecher who took downhill bronze medals at the 1960 Squaw Valley and 1964 Innsbruck Games.
"It's incredible, one of the most emotional moments in my life," Vonn said of her first medal in three Olympics.
"To come into the finish area and see my name and Julia's up there was amazing."
Sweden's Anja Paerson had the silver within her grasp when she crashed heavily off the final jump, flying 58 metres through the air before landing hard on her rear and ending up face down.
Vonn gasped, covered her mouth and looked away.
Paerson was helped off the piste by doctors, one of several fallers. A Swedish team official said the Olympic slalom champion had a bruised left calf but nothing broken.
With the sun shining and clear skies replacing the fog and snow that hit the schedule earlier in the week, Vonn blew kisses to her family and friends in 'Vonncouver' hats as she watched rivals fall or fail to match her time.
"I knew what I had to do, I knew what type of run I needed to take. I had to attack and I did that," she added. "I made it down. It's awesome, it's all I ever wanted."
Vonn had won five out of six World Cup downhills this season and had the perfect setting to show once more that she was in a class of her own despite the injury that had threatened her participation in the Games.
Germany's Maria Riesch, Vonn's best friend and main rival, failed to produce her best and finished well out of the medals, more than two seconds slower.
"I was little bit too conservative for that bumpy and challenging course and of course the external factors were not good for me. I knew that lots of people crashed," she said.
Britain's Chemmy Alcott finished 13th overall, just a third of a second off a place in the top ten.
Czech Klara Krizova was the first skier out of the starting hut and set the tone for what was to follow when she snagged a gate and fell.
Switzerland's Dominique Gisin went out in tears after ending up in a crumpled heap after flying off the final jump. She was followed by Italian Daniela Merighetti, plunging headfirst at the same place.
Vonn, who had complained after training on Monday that the Franz's run was too bumpy, had to follow them down but there was never any doubt about her steely determination and poise.
She was already 0.43 seconds quicker than Mancuso, the reigning Olympic giant slalom champion who was waiting at the finish with a glittering tiara in her hair and tears in her eyes, at the second intermediate and 0.83 at the third.
Mancuso said: "I kind of enjoyed the bumps because it was more mentally tough - you had to stand on your downhill ski and just go for it.
"I watched a lot of video and focused on how I could be fast here," she said. "I love this course, it's hard and fast and I just knew I could go out there and put my all into it."
Mancuso's last time on the podium was also in Whistler in a World Cup race two years ago, and her career has been slowed by injury since then.
Romania's Edith Miklos was a late faller and had to be winched off the mountain by helicopter, the sound of rotors drowning out the cowbells as Vonn celebrated.
While four years of training resulted in a four-second flop for France's Marion Rolland, the victim of an embarrassing spill just moments after leaving the starting gate.
Rolland dug her poles into the piste four times over the first few meters before she suddenly lost her balance and tumbled onto her right side as her left arm waved wildly in the air. To make matters worse, the 27-year-old injured her knee in the process.