Long known for his careful yet lucid prose, Mackintosh's publication in 1991, with Jens Jensen, of Rare Earth Magnetism, was a landmark in solid state physics and the book became a classic text. In the same year he was elected Fellow of the Royal Society. In Denmark, he was made a Knight of the Dannebrog Order. He was also a Fellow of the Royal Danish Academy of Sciences and Letters, the Danish Academy of Technical Sciences [ da ], the Royal Norwegian Scientific Academy, and the American Physical Society. Uppsala University awarded him an honorary doctorate of philosophy in 1980.