In her youth Hattestad was a very good handball player, but then changed her javelin. Her international debut was Hattestad 1981 at the Junior European Championships, where she finished fifth.
However, the really big successes came only in the early 1990s. At the World Championships in Stuttgart in 1993, she won gold, as well as at the European Athletics Championships in Helsinki in 1994. At the Olympic Games in Atlanta in 1996, she won the bronze medal. The following year, she defended at the World Cup title in Athens. At the World Cup in 1999 in Seville, she won bronze.
2000 was its most successful year: On June 28, she scored in Bergen a world record; she threw the javelin 69.48 meters. This length was exceeded almost a year later by the Cuban Osleidys Menéndez two meters. At the Olympic Games in Sydney she won the javelin competition and thus crowned her successful sports career. In the same year she won the election to Europe's athlete of the year, Norway's athlete of the year, the Aftenposten gold medal as well as the Fearnleys olympiske ærespris.
She is married to Anders Hattestad and has four children.