Kranjec was born in Ljubljana, Slovenia. His first victory in a World Cup competition was at Kuusamo, Finland in 2005. The following years he could not reach any top results except for ski flying competitions. In 2010 he celebrated his second World Cup victory at Tauplitz, Austria. After two more successful ski flying competitions at Tauplitz and Oberstdorf, in which he achieved the second place each time, he won the ski flying World Cup 2009/10.
Kranjec's most successful season was 2011–12. Apart from becoming the World champion in ski flying and winning the bronze medal in team competition at the 2012 Ski-Flying World Championship, he won two competitions in World Cup. Together with two additional podiums, Kranjec won the second ski flying World Cup in his career.