The 29-year-old veteran of the sport was not among the top favorites in the event and he needed two attempts to qualify for the three-stage final portion of the aerials.
He managed a second-place finish in the first stage of the finals and was third in the second stage behind two Chinese competitors.
Under the format used in freestyle skiing events at this year's Olympics, however, all of that was thrown out when the last four standing competed in the third stage of the finals.
No matter what has happened before, the judges' score in the last round determines who wins the medals and Kushnir's total of 134.50 was the best turned in by anyone all day.
David Morris of Australia was second with a score of 110.41 and Jia Zongyang of China was third at 95.06.
Qi Guangpu of China needed only one round to qualify, then had the best score in the first final stage and the second best score in the second stage. When the pressure was greatest, however, he finished fourth and last in his final trip down the course with a score of 90.00.
Kushnir added to the amazing medal total being compiled at these Olympics by athletes from Belarus.
Prior to these Games, Belarus had grabbed only one Winter Olympics gold medal. There have been five at the Sochi Olympics, three from biathlete Darya Dormacheva. Alla Tsuper of Belarus also won gold in the women's aerials.