He competed at the 1952 Winter Olympics in the Nordic combined and 18 km cross-country skiing and won the gold medal in the former event.

Earlier he won a Nordic combined bronze medal at the 1950 World Championships.

He won 14 Norwegian titles and was the first Nordic combined athlete to jump over 100 m. Slåttvik won the Nordic combined event at the Holmenkollen ski festival in 1948, 1950 and 1951, and was awarded the Holmenkollen medal in 1951.

His career was delayed by World War II and peaked around 1950, when he was already in his thirties.

After the 1952 Olympics he won a national title in 1953, placed fifth at the 1954 World Championships, and remained active through the late 1950s.