Going into the Finals race, Ligety knew victory in Switzerland would mean Hirscher had to finish higher than fourth to deny him a fifth men's giant slalom crystal globe.
Austrian Hirscher had however finished on the podium in six out of seven giant slalom races this season and posted a time of 2:15.90minutes from his two runs to leave him well placed ahead of the final racers.
But Ligety, leaving the gate as the penultimate racer, finished in 2:15.63 to take the lead ahead of France's Alexis Pinturault and edge Hirscher into third.
That left just Felix Neureuther to go, and the German did Ligety a favour, finishing just 0.01secs faster than Hirscher to push him into fourth.
It left Ligety and Hirscher tied for 560 points this season but with former having claimed five giant slalom wins to Hirscher's two, it was the American who took the title.
Hirscher however clinched a third straight overall World Cup title after securing the 19 points required to overtake Aksel Lund Swindal of Norway.
Meanwhile Mikaela Shiffrin capped off a fine alpine season by taking victory in the women's slalom and equal the American record for most World Cup slalom wins with nine.
Shiffrin, who had already secured the slalom crystal globe for the second successive year, became the first woman to win the Lenzerheide slalom twice when she posted a time of 2:04.54mins from her two runs.
It saw her take victory by 1.44secs ahead of Sweden's Frida Hansdotter and Austria's Marlies Schild with the pair finishing in the same order behind slalom Olympic gold medallist Shiffrin in the world cup slalom standings.
� Sportsbeat 2014
- Sports & Recreation
- giant slalom