Education
He finished fifth at the 1986 European Championships, fifth at the 1987 World Indoor Championships, tenth at the 1990 European Indoor Championships, sixth at the 1990 European Championships and fifth at the 1991 World Indoor Championships.
Career
He represented Urædd Friidrett. Nilsen"s last international competition was the 1992 European Indoor Championships, where he finished seventh. This is the current Norwegian record.
Nilsen was tested for and found to be using banned substances in 1987 and 1992, which led to a lifetime ban from organized sports.
In 2004 he was pardoned and is free to participate in organized sports and competitions in any other sports than shot put. He may not participate in competitions which qualify for national or international championships.