Overshadowed all season by Croatia's Ivica Kostelic and Austria's Marcel Hirscher, he took the discipline's crystal globe after the two favourites crashed out.
"I'm all over the place. It's totally unexpected. I was lucky and I knew I had to expect something special. But there was a chance and I took it," said Myrher, the first Swede crowned in the discipline since Thomas Fogdoe in 1993.
For Hirscher and Kostelic, the last two winners of the overall World Cup, the final race of the season was a sharp anticlimax.
With a solid 66-point lead at the start, Kostelic had looked safe enough but the Croat found himself on his back after only four gates and out of contention even if he made a point of finishing.
"I just don't know what happened. I felt good and all of a sudden I found myself on my backside," said the 2011 World Cup champion, who lost everything this season after a knee injury again broke his momentum.
Crowned the best skier of the season after his victory in Saturday's giant slalom, Hirscher did not go much further, straddling out halfway down the morning run.
Myhrer did not falter, the 29-year-old finishing the first leg second fastest behind German Felix Neureuther before winning in a combined time of one minute and 32.47 seconds.
Neureuther was second, 0.30 adrift and veteran Austrian Mario Matt third, 0.60 behind.
Myhrer, a popular character on the ski circuit who often entertains post-race parties with his heavy metal band, is the third Swede crowned in the discipline after Ingemar Stenmark and Fogdoe.
The Swede ended up with 644 points to Kostelic's 610 and Hirscher's 560.
"It's a great reward for all the hard work. I had decided to improve my consistency this season and it paid off," he said.
In the finish area, he paid homage to the two prominent retiring skiers of the season, by attempting a ski flip in the style of Didier Cuche before emulating compatriot Anja Paerson's trademark walrus slide.
Only 14 skiers finished inside the time limit in the final slalom, raising questions about the decision by Beat Feuz to shun the race as the Swiss might have scored points to challenge Hirscher.
Swiss team sources said Feuz did not want to take any chances, however ,after struggling with knee problems for most of the end of the season for which he will receive surgery next week.