Jón was born in Grundarfjordur in 1862 and went on to study at Reykjavík Grammar School and then the University of Copenhagen.
[2] In October 1918 he married a widowed French Mauritian woman, Adrienne de Chazal.
Shortly after their marriage they moved to Mauritius but Jon became ill and returned to Iceland and then back to London.
In London he spent much of his time in the British Museum writing but he was also an acquaintance of a wide range of scholars including William Morris, William Paton Ker, James Bryce and Israel Gollancz.
In London he worked for a few years as a lecturer in Icelandic and Danish at King's College.