Robert Kranjec achieved his first success in the world elite at the 2002 Winter Olympics in Salt Lake City with a bronze medal in the team competition. A few years followed with placements in the midfield. His first World Cup victory was at the beginning of the 2005/06 season in Kuusamo, Finland . Since this was the first event in the World Cup, he was briefly wearing the yellow jersey of the World Cup leader. There followed more unsuccessful years in which he was mostly only able to achieve top positions in ski flying. At the Slovenian Ski Jumping Championships in 2009 , Kranjec won the championship on the large hill. On January 9, 2010, he was able to take his second win in ski flying in Tauplitz after surprisingly prevailing against Simon Ammann . In the ski flying competition the following day, he took second place. In Oberstdorf he was able to achieve second place again on January 31 in ski flying, which meant that he was able to secure overall victory in the discipline world cup for ski flying. At the 2010 Olympic Winter Games in Vancouver , he reached 6th place on the normal hill and 9th place on the large hill.
At the Slovenian Championships 2010 in Kranj, Kranjec again won both individual and team titles. At the Nordic World Ski Championships in Oslo in 2011 , he started for Slovenia in all four jumping competitions. From the normal hill he reached the 32nd place in the individual and sixth place with the team. From the large hill he reached the 23rd place in individual jumping. In team jumping he won the bronze medal together with Jurij Tepeš , Jernej Damjan and Peter Prevc . Then, this Slovenian team was in the vote for Sportsman of the Year in their home for Team of the Year chosen. On February 19, 2012, he and the Slovenian team won the team competition on the Heini-Klopfer ski jumping hill . The Slovenian team won a team competition in the World Cup for the first time.
Robert Kranjec is considered one of the best ski flyers on the scene. On the ski jumping hill in Planica he had a very serious fall in 1999, in which he was seriously injured after a jump mistake. He celebrated his greatest success in flying with victory in the individual at the Ski Flying World Championships 2012 in Vikersund , where he also set his new personal best of 244 meters. In the team competition, he won the bronze medal with the Slovenian team behind Austria and Germany. On March 16, 2012 he was the first Slovene to win a ski flying on Letalnica bratov Gorišek in Planica.
In the 2014/15 Ski Jumping World Cup, Kranjec performed significantly worse than in previous years and often failed to jump into the second round. His best individual placement of the season was a tenth place in Lillehammer . He finally finished the overall World Cup in 26th place. On March 21, 2015, he won the team competition with the Slovenian team on his home hill in Planica . In the following season he was able to improve his form again, with two individual victories (Vikersund and Planica) and a team success in Oslo in the 2015/16 Ski Jumping World Cup .
During the preparation for the 2016/17 Ski Jumping World Cup , Kranjec sustained a cruciate ligament injury on his right knee. At first he continued his training, but a few weeks before the start of the season he announced on Facebook that he was going to have an operation and that he would not jump in the 2016/17 season. According to its own statements, Kranjec wants to take the time to heal the injury in order to focus on the 2018 Winter Olympics .
Shortly before the second Planica 7 event in March 2019, Kranjec announced that it would end his career after ski flying from Letalnica bratov Gorišek . On March 21st, he only finished 47th in the qualification for Planica 7 and thus missed the individual competition. This was his last competition jump. On March 23, he made his farewell jump after the first round of the team competition, in which he reached a distance of 213.5 meters.