Winner of his first World Cup slalom in mid-January in Flachau, the 29-year-old skier edged the surprising Austrian Adrian Pertl (at 0''21), in the lead at the end of the first round, and his compatriot Henrik Kristoffersen (0''46).
He won his first individual world title, after the collective coronation won on the team parallel on Wednesday.
“It was a battle from the start at the bottom of the track, and I won!” Exclaimed the winner at the finish.
Third at the end of the first race, Foss-Solevaag managed to avoid the pitfalls of a bouncy track, which trapped Clément Noël and Marco Schwarz in particular.
Leader of the Slalom World Cup standings, the Austrian straddled in the second round.
Offensive from the first gates, Noël also missed a turn at the end of the course and is still running behind his first medal at the World Championships.
In the World Cup, the Vosges skier has already won seven slaloms in three winters.
Starting just after Schwarz, the French leader of the big globe race Alexis Pinturault finished 7th (at 1''50), before Kristoffersen set a first benchmark time.
But three starts later, it was Foss-Solevaag who set the fastest time.
Much to his joy, the Norwegian raised his arms high before entering into the protective barriers of the finish area.
A small fall without consequence.
For this last event of the World Championships, the traditional hierarchy of slalom was upset by the generous Italian sun, which degraded the snow.
Norway did well, in a season darkened by the injury to the right knee of the last winner of the big globe, Aleksander Aamodt Kilde, and the poor performance of Kristoffersen, seventh in the World Cup standings.
A specialist in slalom, the only discipline in which he competes in the World Cup, Foss-Solevaag on Sunday offered Norway their first world gold medal in slalom since 1997 and the victory of Tom Stiansen in Sestriere, already in Italy.
The last Norwegian to be on a slalom podium at the World Championships was until Sunday Lasse Kjus, 2nd in 1999 at Beaver Creek.
With his 2nd place, Pertl won at 24 the first medal of his career at the World Championships.
His best result so far was a third place, won in early February in the slalom during the World Cup stage in Chamonix.
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