Johnstone, 21, won the Freestyle Snowboard Overall World Cup title and also headed the end of season points tally in halfpipe, to become the first Australian snowboarder to take home two Crystal Globe trophies, the ultimate prize in World Cup competition, in the one season.
It rounds out a highly successful 24-hour period for Australian snowboarders in Arosa, Switzerland, after Alex "Chumpy" Pullin won the final event of the snowboard cross season to finish his year with the number one world ranking.
Johnstone's halfpipe team mate Holly Crawford was runner-up in the final round of competition to finish the season ranked second, the best result of her career.
Johnstone, from NSW's Perisher, won the overall title by 550 points ahead of Austrian Clemens Schattschneider and the halfpipe by 710 points, in front of Japanese rider Ryo Aono.
The NSW Institute of Sport and Australian Institute of Sport scholarship holder was predictably jubilant after the season ending event in Arosa, where he placed fifth, behind Swiss trio Iouri Podladtchiko, Jan Scherrer and Patrick Burgener, who filled the podium places.
"At the beginning of the season I really wanted to get that Globe and I've finally got two of them, it's amazing," Johnstone said.
"It would have been nice to have done a little bit better today but I'm still happy with fifth.
"Winning the overall was the icing on the cake with the season."
Johnstone has achieved the world number one ranking after just 15 starts at World Cup level and seems headed towards an even brighter future in terms of further success, on and off the snow.
He has yet to contemplate what the titles will do for his career but is pleased with the knowledge that he is contributing back to his sport.
"Hopefully this will help with funding and more media coverage of snowboarding in Australia. I think it will do a lot of good things."
Johnstone is looking forward to returning home to Australia after a grueling season and plans to take a few weeks off "hanging out with friends" before sitting down with his coach Ben Alexander to work out the goals for the next stage of his march towards the 2014 Winter Olympic Games in Sochi, Russia.
Crawford also shared in a season to remember by finishing in second place in the World Cup Halfpipe and Freestyle Overall titles, 500 points behind China's Xuetong Cai in both categories.
In a season that should not be overlooked by Johnstone's and Pullin's titles, the Sydneysider delivered brilliant results all year.
Crawford backed up a win in the previous World Cup round with a second in the season ender in Arosa behind Spain's Queralt Castellet, who recorded her first World Cup win.
Crawford needed to out-score her Chinese rival by more than 700 points last night, but with Cai finishing in third place, Crawford's task was impossible.
However, finishing the year as the number two ranked halfpiper and winning the World Championship in Spain in January has clearly establish her as one of the elite in her sport.