At the 1980 Olympics in Lake Placid, New York, Siebert won a silver medal on the relay with the East German relay team.

[1] In the Biathlon World Championships, Siebert earned two gold medals with the East German relay team in 1978 and 1979, and a bronze medal from 1977.

He returned to his coaching role with the Belarusian national biathlon team in January 2012 after spending much of the previous year ill with cancer.

[2] However, Siebert stepped down from this role ahead of the 2014-15 season due to health issues.

[3] Siebert died in Altenberg, Germany on 24 April 2016 after a long battle with cancer at age 60.