It's the American's fourth GS season title after also winning in 2008 and 2010-11. He also successfully defended his GS title at the world championships last month.
"To win here again is a super cool feeling," said Ligety, who has won in Kranjska Gora five times and been on the podium every year since 2008. "I am really proud of that."
Ligety held on to his first-run lead to win Saturday's race in 2 minutes, 35.43 seconds for his 16th career victory, all in GS.
The victory earned Ligety an insurmountable 125-point lead over Austria's Marcel Hirscher, who was 0.45 behind in second. Hirscher had beaten Ligety for the GS title a year ago.
The last GS of the season takes place next Saturday during the World Cup finals in Lenzerheide, Switzerland.
"It's a big weight off my shoulders," Ligety said. "I had an awesome, awesome season but Hirscher was there all the time. Even if I beat him by three seconds, he was still in second place. That makes it tough going for the title. It becomes kind of a head game when he is so close all the time. So I am pretty psyched to have it locked up now."
Ligety took the season-opener in October by a massive 2.75-second margin, setting the tone for his dominant GS campaign. He has finished on the podium in all seven races this season and became the first man to achieve that feat since Michael von Gruenigen of Switzerland in 1995-96.
"It's certainly something I don't expect to replicate because it's been a dream season in giant slalom," Ligety said. "I have been winning races by good margins, sometimes by two seconds, but you don't get extra points for that. That's why Marcel in second place has been so close all the time."
Alexis Pinturault of France came third, 0.77 behind, and Felix Neureuther of Germany placed fourth, 0.81 off Ligety's time.
In the overall standings, Hirscher extended his lead to 69 points over Norway's Aksel Lund Svindal, who finished sixth.
Hirscher had already written off his chances of retaining his GS title weeks ago because of Ligety's dominance. The Austrian said he has been focusing on winning the slalom title and defending his overall championship.
"These 80 points are very important for me," said Hirscher, who was fourth after the opening run before reducing his deficit to Ligety by 0.15.
"My second run was really good," Hirscher said. "If you can beat Ted Ligety in the second run it is always a very awesome run."
Rain made for difficult conditions during the final run on a course that already been softenened by days of mild temperatures.
"Racing in the rain is not my favourite thing," Ligety said. "I grew up in Park City, Utah, where it's usually warm and sunny. These are totally different conditions."
Ligety led Hirscher by 0.60 after the opening run, in which the Austrian placed fourth behind Pinturault and Neureuther.
"The snow is really soft," Ligety said. "It's hard to keep your edge in the snow well. It didn't feel good at all. This is a very difficult course set, especially for how the snow is running. It was tough to have a good feeling."
The course for the first run was set by Austrian slalom coach Michael Pircher. He designed numerous sharp turns, an unusual feature for a GS and one that didn't benefit Hirscher.
"We thought — and that was a big mistake — that Aksel could not go nearly the same speed as we specialists on this course," Hirscher said. "But he was awesome. We thought it would be very challenging for Aksel but it was wrong thinking."
Svindal finished the opening run just 0.39 behind Hirscher in fifth place.
Fritz Dopfer, who was seventh after the opening run, crashed out after his goggles came off when he hit a gate with his helmet. The German landed in the safety netting but appeared unhurt.
A men's slalom on the same course is scheduled for Sunday. If Hirscher finishes the race 14th or better, the Austrian wins the season's slalom title.