Fontana took first place in the women's 500 metres event in Pyeongchang on Tuesday, with Choi Min-jeong of South Korea so close behind it was a photo finish.
Choi was disqualified, leaving Yara Van Kerkhof of the Netherlands and Canada's Kim Boutin with silver and bronze respectively.
Fontana, Choi and Boutin. Photo: Roberto Schmidt/AFP
"I was a long journey, more beautiful than I had imagined," said Fontana, who has four Olympic bronzes and one silver from previous games. "It's a dream come true. I've been chasing this gold for years. It feels wonderful to have crossed the finish line ahead of [Choi] on her home turf."
The effort earned Fontana, who carried the Italian flag in the Pyeongchang opening ceremony, the congratulations of Prime Minister Paolo Gentiloni.
Grande Arianna #Fontana primo oro olimpico italiano👏👏— Paolo Gentiloni (@PaoloGentiloni) February 13, 2018
Italy also got its first silver of the games on Tuesday: it went to skier Federico Pellegrino in the men's cross country sprint.
"I wanted a medal at all costs," said Pellegrino, who narrowly overtook Alexander Bolshunov of Russia for second place, behind Norway's Høsflot Klæbo in first.
Italy currently has one medal of each colour, thanks to a bronze for Dominik Windisch in the men's biathlon 10 km sprint.
Team Italia is hoping to pick up some more in the women's alpine skiing events, while 22-year-old Michela Moioli is one of the favourites to win the snowboard cross.