In 2004/05, he achieved three podium finishes in World Cup Sprint events, including a win at Reit im Winkl. He finished the season in 10th, 235 points behind overall winner Axel Teichmann. He was 62nd in the distance standings, 520 points behind Teichmann, and came second in the sprint discipline, 237 points behind fellow countryman Tor Arne Hetland. He also came second in the sprint discipline at the Norwegian national championships.
Rønning shared the 2005/06 season between the World Cup and the Scandinavian Cup, competing almost exclusively in sprints. He only competed in one World Cup race that was not either a sprint or a pursuit, it was a 15km classic style race in Davos, Rønning finished 30th, 1:25.9 behind winner Jens Arne Svartedal. His best World Cup result was a third place avchieved in a classic sprint in Drammen, a race in which the top four were Norwegian, and was won again by Svartedal. Rønning also came fifth twice, both in sprints, his only other race in the World Cup when he finished inside the top 20, was a 16th place in a sprint, in Oberstdorf. Rønning finished the season in 11th place in the FIS World Cup overall standings, 474 points behind GermanTobias Angerer. Rønning was 28th in the distance standings, 671 points behind Angerer, and 7th in the sprint standings, 349 points behind sprint winner Björn Lind.
Rønning has won 6 world cup races (15 km classical – 3 times, classical sprint – twice, and freestyle sprint) and 3 world cup stages (all in Tour de Ski, 30 km classical mass start, 20 km classical mass start, classical sprint). In addition he has 8 individual world cup podiums.