Aged 19, Eirik Kvalfoss was fourth in the 10 km sprint at the 1979 World Junior Championships. Two years later he won his first World Cup victory in Anterselva, Italy. He was 1982 World Champion in the 10 km sprint in Minsk, where he placed second in the 20 km and won another silver medal in the relay. He defended his world sprint title at Anterselva in 1983. In the 1984 Sarajveo Olympics he again won the sprint, placing third at 20 km despite five penalty minutes, and he earned a silver in the relay. From 1982-91 Kvalfoss was world champion three times (his third gold came in the 1989 20 km) and had five silver medals and five bronze medals. In the Olympics however, although competing again in 1988 and 1992, he was not able to win more medals after his 1984 success.
Kvalfoss used a couple of seasons to adapt to the skating technique introduced in 1985, and five of his 12 World Cup victories came in the period 1988-91 with the new technique. He won the World Cup in the 1989/90-season, and was known for his ability to give all he had at the final stage of a race. Kvalfoss was Norwegian champion nine times. He carried the Norwegian flag at the 1992 Opening Ceremony in Albertville, but failed to qualify for the 1994 Lillehammer Games and then ended his biathlon career. Kvalfoss married in 1994, settled in Oslo and has worked in the insurance business as a marketing manager.