Theaux mastered windy conditions to race down the steep 1.64-mile course in 1 minute, 29.10 seconds and beat Svindal by 0.19 seconds. Klaus Kroell of Austria was 0.50 seconds back in third. The Frenchman's only previous win came in March 2011 in Switzerland.
The race had been threatened by stormy weather from Scandinavia, but the gusts over the Kvittfjell course were not as strong as expected.
The wind was still strong enough to make it difficult for the racers, Theaux said.
"I think the trick was to try to keep your tuck as much as possible and avoid catching more wind than necessary," Theaux said. "I am really happy also as this has been my first downhill this year without mistakes, everything came together today. Conditions were not easy but all of us on the podium are among the top downhill skiers, so I am happy to be sharing this result with such good skiers."
The top Americans were Travis Ganong in 16th place and Marco Sullivan in 23rd.
Svindal's second-place finish meant he made up some ground on overall World Cup leader Marcel Hirscher and trails the Austrian by 129 points. The Norwegian also extended his lead over Kroell in the downhill standings — but is still looking for his first victory in Kvittfjell despite having six career podium finishes here.
"I would obviously like to win here someday and I know it will come sooner or later, but for that I need to just ski faster so today this is a good second place," Svindal said. "I do have a lot of podiums here, but somehow there is just always someone that is better on this slope."
The downhill is followed by a super-G on Sunday.
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