Choi was the fastest among seven skaters after the 13.5-lap finals at the Gangneung Ice Arena. She crossed the finish line at 2:24.948, well ahead of Li Jinyu of China and Kim Boutin of Canada.
With Choi's gold, South Korea has three golds in total, with two from short track and one from skeleton.
Her teammate Kim A-lang finished fourth.
Choi, the current world No. 1 in the 1,500m, was dominant, showing her acceleration in the latter part of the run.
She skated at the back until the 11th lap and she kicked into another gear with two laps to go. From fourth place, she shot up to first place and extended her lead over the field. She crossed the finish line with no one close to her.
"Short track is unpredictable. There are many changes and surprises in the race. So I wasn't sure until crossing the finish line," Choi said, explaining why she remained keen until the end of the race after losing a medal in the 500m event on Tuesday due to an impeding penalty.
It is the first time in 12 years that South Korea has won the women's 1,500m title at the Olympics. The discipline had been led by China since South Korean Jin Sun-yu topped the race at Torino 2006.
As the 19-year-old swept the No. 1 ranking in all individual short track races -- the 500m, 1,000m and 1,500m -- for the 2017-2018 season, she had been regarded as the strongest hopeful to bring home the title and win gold.
"It's something that athletes have to deal with. I knew I was well prepared, and I decided to just skate without getting caught up in the results," Choi said of the pressure that she has felt for years. "I could have not made it if I raced alone. So many people supported me and gave energy to me. I'm so grateful to those who trust me."