In 1992, Hefting completed his studies in Archaeology at the University of Amsterdam. Throughout his career, he specialized in Dutch fortifications overseas. He was a staff member of the Dutch-Brazilian team that conducted excavations around Fort Oranje on the island of Itamaracá, where a complete 17th-century Dutch fort emerged beneath an 18th-century Portuguese fortification.

As director of the NHF, he coordinates inventories of historical and archaeological materials for the Atlas of Dutch Brazil, the Atlas of Dutch North America, and the Atlas of Dutch West Africa. The research findings are incorporated into the Atlas of Mutual Heritage. In his role, he promotes research, publications, exhibitions, and the preservation of Dutch heritage overseas.

For Historizon, Oscar is organizing trips to New Netherland (2025) and Dutch Brazil (2026).