Michael Thelvén took up hockey in 1978 with Djurgårdens IF and played there until 1985. With Djurgårdens, he won the 1983 Swedish title and was selected to the Swedish championships all-star team in 1984 and 1985. Thelvén was drafted by the Boston Bruins of the NHL in 1980 and joined the team in 1985, playing the next five seasons and 207 games with them. Thelvén retired from hockey in 1990 after a serious knee injury. Internationally, Thelvén was capped 67 times with the Swedish national team. He won Olympic bronze in 1984 and was a runner-up at the 1984 Canada Cup. He also played at the 1985 World Championships and 1987 Canada Cup.