At that time, he became the first person in Oslo to receive a scholarship from the Norwegian General Research Council (NAVF).
In 1974, Nygaard earned his doctorate in jurisprudence for his dissertation "Aktløysevurderinga i norsk rettspraksis" ("the Culpa-norm according to Norwegian case law").
Alongside Gudrun Holgersen, with whom he co-authored several books, Nygaard contributed to the development of the field of Norwegian social security law.
Nygaard has a significant body of academic literature to his name, particularly in the fields of tort and social security law.
Nygaard was also the author of a substantial collection of articles covering topics ranging from insurance, suicide and mental illness to the state's liability for errors or omissions in implementing EU/EEA directives.