Marit Myrmæl had her breakthrough in 1976 when she was Norwegian Champion in the 5 km race, earning a place on the Olympic team for Innsbruck. She won three more national titles (1979 10 km and 1977/79 20 km), and won an Olympic bronze medal as a member of the Norwegian relay team in 1980. She had a good season in 1982 when she placed sixth in the World Championships in 20 km classical, and placed second at the same distance in the World Cup races at Falun, Sweden. Myrmæl was selected for her third Olympics in 1984, where she placed seventh in the 10 km race, her best individual Olympic result. She was also an excellent cross-country runner, winning the 1978 national championships over 10 km.
After her career, Myrmæl worked for the Norwegian Olympic Committee and Association for Sport, later becoming manager for the international department of the Norwegian NOC. She worked as chief of sports for the 1997 World Nordic Ski Championships in Trondheim.