From December 2007, at the age of 15, Kranjec took part in FIS races and national junior races. In February 2009 he was a participant in the European Youth Olympic Festival in Szczyrk , where an 11th place was his best result. Two months later he was able to win an FIS race for the first time. The first use in the European Cup followed in March 2010 . In February 2011 he became the Slovenian giant slalom junior champion. A week later, on March 5, 2011, Kranjec made his debut in the World Cup ; while he finished the giant slalom of Kranjska Gora in 42nd place. During the 2011/12 season he gradually established himself in the European Cup. Shortly after becoming Slovenian junior slalom champion, he won bronze medals in giant slalom and combined at the 2012 Junior World Championships .
Although he did not yet have a countable result in the World Cup, Kranjec took part in the 2013 World Championships in Schladming and finished 22nd in the giant slalom. At the Junior World Championships in 2013 he won two more medals, gold in the team competition and bronze in the giant slalom. He won his first World Cup points on December 23, 2013 with 23rd place in the giant slalom on the Gran Risa in Alta Badia . In the European Cup he achieved his first podium finish on December 3rd, and on January 26th and 27th 2014 he won two giant slaloms in a row. With this he decided the giant slalom discipline ranking for himself.
From the winter of 2015/16 onwards, Kranjec regularly achieved placements among the top 20. At the beginning of the 2016/17 World Cup season, he was classified twice as fourth, on October 23, 2016 in Sölden and on December 18, 2016 in Beaver Creek . In the further course of the season, however, he could not quite maintain this level. After another top 10 placement at the beginning of the 2017/18 season, he finished third in the giant slalom in Alta Badia on December 17, 2017 , which was synonymous with his first podium finish in a World Cup race. He achieved his first World Cup victory a year later on December 19, 2018 in the giant slalom in Saalbach-Hinterglemm .