Ulvang began skiing competitively at the age of 10 and joined the World Cup circuit in 1984. He won a bronze medal in the 30-km event at the 1988 Olympics in Calgary, Alberta, Canada. He won the Holmenkollen 50-km race in 1989 and was the World Cup overall champion in 1990. At the 1992 Winter Olympics in Albertville, France, he won three gold medals (10-km event, 30-km event, and 4×10-km relay) and one silver (combined pursuit). His win in the 30-km event was significant as the first Olympic gold for a Norwegian male cross-country skier in 16 years, and his time of 1 h 22 min 27.8 sec set a new record for the event. He was unable to repeat his spectacular performance before his compatriots at the 1994 Winter Olympics in Lillehammer, Norway, because of an injured left hip and the emotional strain of searching for his brother Ketil, who had disappeared while jogging four months prior to the Games and was presumed dead. Ulvang managed only a silver medal in the 4×10-km relay. His brother's body was discovered four months later.

Ulvang retired after the 1996–97 World Cup season as one of the most successful and popular Norwegian skiers ever. He was chosen by his country to deliver the Olympic oath at the 1994 Winter Olympics, and his success at the 1992 Olympics prompted Kirkenes' merchants to buy him a mountain cottage and the Scandinavian Airlines System (SAS) to rename a plane Vegard Viking.