In 1981, Mirzoyan became a member of the USSR national weightlifting team. Mirzoyan became a European and World Champion in 1983 by winning gold medals at the 1983 World Weightlifting Championships and 1983 European Weightlifting Championships, both in Moscow. In the course of both the competitions, Mirzoyan set new world records in the snatch, clean and jerk and the total exercise, all in the bantamweight (56 kg) division. Due to the 1984 Summer Olympics boycott, Mirzoyan was unable to participate that year. As the reigning World Champion, he would have been the favorite to win the Olympic gold medal.