The 20-year-old launched into a massive jump with her final trick to earn a winning score of 92.88, before being mobbed at the finish by Marino and bronze-medallist Tess Coady of Australia.
A large New Zealand flag and another bearing the country’s black fern symbol could be seen among the crowd.
New Zealand had previously won one silver and two bronze medals at the Winter Olympics — including a third-place finish for Sadowski Synnott in the Big Air competition at the 2018 Pyeongchang Games.
Sadowski Synnott dazzled the judges by grinding along rails, leaping off huge jumps and sliding along the roof of a traditional Chinese house made from snow en route to the gold.
Marino finished second on 87.68 points, while Coady took bronze on 84.15.
Two-time defending champion Jamie Anderson of the United States finished well out of the running in ninth place on 60.78 points.