Jonas Nilsson was Junior European Champion in Slalom in 1981 . He won his first points in the World Cup on December 2, 1983 with sixth place in the slalom of Kranjska Gora . After two more top 10 results, he reached fourth place in slalom at the 1984 Winter Olympics in Sarajevo . He was only five hundredths of a second short of a medal. Nilsson achieved his first podium places in the World Cup in the 1984/85 season with two second places in the slaloms of Sestriere and La Mongie and a third place in Kranjska Gora, making him among the top ten in the Slalom World Cup for the first time and there for the next five years stayed. In 1985 he was also the first Swedish champion in slalom. He was able to repeat this success in 1989 and in 1990 he became the Swedish champion in giant slalom. The then 21-year-old celebrated the greatest success of his career at the 1985 World Cup in Bormio . On the Pista Stelvio, Nilsson beat season dominator Marc Girardelli , who won seven of the ten World Cup slaloms this winter and was in the lead after the first run, with the fastest time in the second run by six hundredths of a second and became world champion in slalom.
On December 16, 1985, Jonas Nilsson stood on the top flight of the podium for the first time in the World Cup when he won the 3-Tre slalom in Madonna di Campiglio . With another three podium places, he reached fifth place in the Slalom World Cup in the 1985/86 season . In the next few years he was able to place himself regularly in the top ten and also achieve a few more podium places. In the 1988/89 season he reached fifth place in the Slalom World Cup with two podium places, while in the winter of 1989/90 he was sixth in the slalom classification with his second World Cup victory in the slalom of Kranjska Gora and a third place in Geilo . After that, Nilsson rarely made it into the top ten and fell significantly behind in the Slalom World Cup. From 1987 he also achieved occasional World Cup points in giant slalom, but never came close to his slalom results in this discipline.
Jonas Nilsson remained without a result at the 1987 World Cup in Crans-Montana . In the slalom, the defending champion was eliminated in the second round and in the giant slalom he failed in race one. At the World Championships in 1989 in Vail / Beaver Creek , Nilsson set the fastest time in the second slalom run, but was already 1.5 seconds behind in the first run, in fifth place, so that despite the best time no improvement in rank was possible. He finished 17th in the giant slalom and 23rd in the combined slalom, with the second best time in the combined slalom, but only 32nd in the combined downhill run. At the 1988 Winter Olympics in Calgary , the Swede achieved sixth place in slalom and 21st place in giant slalom . At the 1991 World Championships in Saalbach-Hinterglemm , Nilsson finished 18th in the giant slalom, while he failed in the slalom after fourth in the first run in the second round. At his last major event, the 1992 Winter Olympics in Albertville , he finished eighth in slalom - eleven months after he was in the top ten for the last time in the World Cup. After the 1991/92 season Jonas Nilsson ended his career.