Ammann proved his victory in Sunday's K90 ski jumping event was no fluke by following it up with a second triumph in Wednesday's K120.
The 20-year-old, competing in his second Winter Olympics, saw off the challenge of favourites Adam Malysz and Sven Hannawald with leaps of 132.5 metres and 133m.
He becomes only the second athlete in Olympic history to win both K90 and K120 events.
Reigning world champion Malysz of Poland won the silver for jumps of 131m and 128m.
Matti Hautamaeki of Finland took the bronze after soaring to 127m and 125.5m.
German Sven Hannawald, who shared the lead with Ammann after the first leap, skidded and fell after landing his second jump and only finished fourth.
Ammann, who was little more than an also-ran coming into the Games, admitted he was as astonished as anyone else by his achievements.
"There are no words for this. I just can't believe it," he said.
"This is a crazy day, a crazy week. I never thought I would win again.
"I really pondered the second jump and what I had to do. I knew that everything was possible but knew that I needed a super-jump to be first," he added.
"It was the best jump I have ever produced in a competition. After take-off I had a wonderful feeling flying through the air and I knew that I had done something special.
"Being the last jumper is more tense. You know everybody has finished. It is a shame that Sven (Hannawald) fell. I feel sorry for him."
For Hannawald, missing out on a medal was a personal disaster.
He won bronze in the K90, but a tally of just one medal from the two individual events will be viewed as scant reward by one of the best athletes in the sport.
Meanwhile, Ammann will get the chance to make it a hat-trick of golds in Monday's team ski jumping event.