Svindal, 35, was seventh out the gate and crossed the line with the fastest time of one minute and 40.25 seconds.
Compatriot Kjetil Jansrud finished second, earning Norway the first one-two in the event in 30 years.
Swiss oust great rivals Austria to win inaugural Alpine team event gold
Svindal adds the Olympic Downhill title to the Super-G gold he won at the Vancouver Winter Olympics in 2010.
Norway's Aksel Lund Svindal reacts after the Men's Downhill 1st training at the Jeongseon Alpine Center during the Pyeongchang 2018 Winter Olympic Games
Image credit: Getty Images
Italy's Dominik Paris set the lead early from the third run but was soon overtaken by Switzerland's Beat Feuz, who was pushed back into bronze medal position by the Norwegian skiers.
Svindal, a five-time World Champion, was slow out of the gates but his speed picked up on the bottom half of the course to post the winning time.
He nervously watched on as his close friend Jansrud produced a storming run of his own, but the 32-year-old was two tenths of a second short of snatching the top prize.
Svindal's Downhill success is the first time Norway have won gold in the event since 1948.