Halldór Hermannsson was born on 6 January 1878 at Völlur, Rangárvellir, in southwest Iceland, to a well-read family. He commenced study of law in Copenhagen after graduation from high school, but soon met Willard Fiske, who was seeking young Icelanders to assist him with his Icelandic collection.
The organization and development of the Fiske Icelandic Collection owe their success principally to Halldór Hermannsson, the first curator.