Siebert won a silver medal at the 1980 Olympics in Lake Placid, New York on the relay with the East German relay team. In the Biathlon World Championships, Siebert has two gold medals with the East German relay team in 1978 and 1979, and a bronze medal from 1977. He also has three individual medals gold medal from the 20 km in 1978 and two bronzes from the 10 km in 1975 and 1978.