The 23-year-old Austrian had already earned his first crystal globe when won the last giant slalom of the winter in a combined time of two minutes 25.53 seconds.
With only Sunday's slalom left, Hirscher had a 25-point lead in the overall standings over Feuz but the Swiss, who struggles in technical events, said before the team captains' meeting he would not take part in the race.
"I don't stand a chance now," he was quoted as saying by Swiss men's team chief Osi Inglin.
As a result, Hirscher became the fifth Austrian to win the overall title after Franz Klammer, Stephan Eberharter, Hermann Maier and Benjamin Raich.
"I'm surprised about Beat's decision not to race. I've been on the podium of the slalom with him at the junior worlds in 2007 and I know he's capable of skiing well in slalom. He had the talent to score points," Hirscher said.
He is also still in contention with Croatia's Ivica Kostelic for the slalom World Cup and could finish off the season in style in front of his home crowd on the final day of competition.
The last giant slalom was an all-Austrian affair, with Hannes Reichelt finishing second and Marcel Mathis taking third place.
"One of my goals is achieved and it's hard to believe. Not that I had any other choice," said Hirscher.
"There was such an awful pressure from the crowd, from my team, that it could not end any other way."
The suspense over the giant slalom title was cut short in the morning run as the only other contender, Ted Ligety, straddled a gate and finished 11.16 seconds off the pace.
American Ligety, the giant slalom world champion, had gone into the day 92 points behind Hirscher and needed to win the race and see the Austrian fail to get into the top 15 to retain his crystal globe in the discipline.
Ligety clocked the fastest time in the afternoon run but the damage was done.
One man was even slower than Ligety in the race: Swiss Didier Cuche bade farewell to competition after 17 years on the circuit by cautiously completing the second leg using ski clothing and equipment dating from before World War Two.