The 28 year old visually-impaired skier, and her guide Charlotte Evans, claimed victory in Sochi by completing the Super-G category in one minute, 28.72 seconds.
It is the first gold medal ever won by the Paralympic GB team.
Kelly and Charlotte were the first entrants on the course and having posted their time had to wait until all the other competitors had completed their timed runs before knowing they had clinched gold.
Kelly had bounced back from the disappointment of finishing last in the downhill, her opening event of Sochi 2014 on Saturday, to win gold in the women's visually impaired super-G on Monday.
Speaking after the event, Kelly said, "I have to thank Charlotte for getting me to the line. We just threw ourselves at it. I prayed for the strength to ski and have fun."
Among those to offer congratulations to Kelly was Prime Minister David Cameron and hundreds of well-wishers in Bangor.