The Aucklander was one of three New Zealand competitors on the podium following the slopestyle finals at Cardrona.
Queenstown's Ruby Andrews secured a silver medal in the women's freeski event and Luca Harrington, of Wanaka, finished third alongside Barclay.
The 17-year-old Barclay set the pace early on as he notched an imposing score of 87.33 courtesy of some varied and complex rail tricks, followed by some well-executed jump tricks.
"I'm over the moon with the win," he said.
"It was a long road after that high score being on my first run. I was pretty anxious throughout, but overall I couldn't ask for a better result."
Wanaka teen Luca Harrington trumped his opening-run score of 80.66 with 83.00 second time down the course as he finished with a huge switch left double cork 1080 safety.
Former junior world champion Taisei Yamamoto, of Japan, also came out of the gate hard and finished second.
His technical rail section and big clean grabs had him well placed, but he lost points for a small bobble on the rails.
In the women's freeski event, Andrews finished in second place, bouncing back from a second-run crash as she landed her top score on her third run, demonstrating well-executed rail tricks.
However, it was China's Eileen Gu who rammed home the advantage on her first trek down the slopes, notching a title-winning score of 88.33.
In the women's snowboarding slopestyle finals, Silje Norendal celebrated her 26th birthday in style as her third-run score of 95.33 sealed victory for the Norwegian.
Japan's Ryoma Kimata won the men's event via a second-run score of 93.33.
