In 1955, young Carl took advantage of the temporary political thaw following Joseph Stalin's death in 1953, obtained a one-month visa to West Germany and biked there, then decided to stay when he learned there that his application to Humboldt University (in East Berlin) for the study of chemistry had been turned down (because of his poor performance in mathematics).

With the support of the Friedrich family, Carl emigrated to the United States in 1959, learning English on his trip across the Atlantic (he could read Beatrix Potter when he boarded the boat).

In 1972, he accepted a position as professor of mathematics and computer science at the University of Wisconsin–Madison, working out of the UW's Army Math Research Center, which had recently been bombed in opposition to the Vietnam War.

A chief attraction of the UW job was the opportunity to work directly with Isaac Schoenberg, considered the father of splines, the piecewise polynomials de Boor would further develop.

Carl de Boor retired from the University of Wisconsin–Madison in 2003 and relocated to the Pacific Northwest, where he continues to work with colleagues on mathematical problems, and to travel.

He was also fed a vast quantity of raw eggs, whipped with a sprinkle of sugar, supposedly to help strengthen him during his early, sickly years.

During his Madison years, he played the bass drum in the neighborhood Fourth of July parade, and each August celebrates his arrival in the United States, where he is a citizen.