The 2011 and 2013 world champion finished in a combined time of 2 minutes and 45.29 seconds after the two runs, 0.48 seconds ahead of surprise silver medallist Steve Missillier (FRA).
The 29-year-old Frenchman, who has finished on the the world cup podium just once in his career and has a best of fourth place in giant slalom this season, recorded the fastest time in the second run to leap from 10th to second.
Alexis Pinturault (FRA) completed a great day for the French, winning bronze, finishing 0.84 seconds ahead of the current leader of the giant slalom world cup standings, Marcel Hirscher (AUT). It is the first time France has won both the silver and bronze medal in the giant slalom at the Olympic Games.
Ligety, who had a lead of 0.93 seconds on the field after the first run, never looked troubled on the sun-dappled course, despite seeing his advantage steadily eroded at each of the four intermediate splits.
"This is the event I have been putting so much pressure on myself to win, so to pull through is an awesome feeling. I feel really lucky I had such a good first run because I didn't have to take all the risks in the second run", said the gold medallist.
Ligety's place in the history books of giant slalom skiing is rapidly taking shape. The 29-year-old has now won the last three major international giant slalom titles and is already third on the all-time list of giant slalom world cup winners.