When in Oslo, he met an American student, Faith Boswell Sloniger, whom he married in Tybjerg, near Næstved, Denmark, in 1961.
In the early 1960s, Ingwersen and his wife moved to the United States, first spending a year at the University of Chicago and then, after he completed his studies in Denmark, the couple moved to Madison in 1965 where he joined the Department of Scandinavian Studies as an assistant professor, becoming a full professor in 1973.
His multimedia course on Hans Christian Andersen attracted a record 873 students, later being offered through the university's public television extension.
[5] In addition to Hans Christian Andersen, Ingwersen's regular courses included Søren Kierkegaard as well as special attention to ballads and folktales, addressing more than 15,000 students over the years.
[4] In the Festschrift in honour of Ingwersen's retirement, Susan Brantly commented: "Niels possesses the rare talent of making complex issues seem simple, and the backbone of his teaching method is telling stories that engage students and get the message across."