As was the case with many of his fellow biathletes, Sumann switched over from cross-country skiing, which he had been doing since childhood.

By the mid-1990s had he entered junior ski team of Austria and later on progressed to senior level.

Sumann began as a biathlete in 2000 and would compete in biathlon at the top level for 11 seasons.

In 2006–07 Biathlon World Cup Sumann won the a mass start race and wore the red bib of the leader of the mass start cup up until the last stage of the season, the fact is quite outstanding for Austrians in biathlon despite the fact that he eventually lost it to Ole Einar Bjørndalen, who thus won the mass start world cup that season.

The 2010–11 Biathlon World Cup was fraught with hardships for Sumann since he caught intestinal disease in Östersund, Sweden in December and he had to combat it throughout the season.