Guðni Th. Jóhannesson was born in Reykjavík on 26 June, 1968. He is the son of Margrét Thorlacius and Jóhannes Sæmundsson; Jóhannes died in 1983. Guðni grew up in Garðabær and has two brothers.
Guðni graduated from secondary school in 1987 in Reykjavík, then studied history and political science at Warwick University in England and finished his B.A. degree in 1991. He studied German at Bonn University in Germany in 1991-1992 and Russian at the University of Iceland in 1993-1994. Guðni graduated with a master’s degree in history from the University of Iceland in 1997. He studied at Oxford University in England and graduated with an M.St. degree in history in 1999. In 2003 he completed his Ph.D. in history from Queen Mary, University of London.
Guðni is married to Eliza Jean Reid, whom he met while they were both studying at Oxford University. Eliza is from Canada and studied modern history at Oxford University and international relations at Trinity College, University of Toronto. Guðni and Eliza have been living in Iceland since 2003. Their children are Duncan Tindur (b. 2007), Donald Gunnar (b. 2009), Sæþór Peter (b. 2011) and Edda Margrét (b. 2013). Rut (b. 1994) is Guðni’s eldest child, from his previous marriage to Elín Haraldsdóttir, business administrator and artist.
Before taking office as President, Guðni was Professor of history at the University of Iceland. He has taught at the University of Iceland, Reykjavik University, Bifröst University and the University of London. For a few years he also worked part-time for the Icelandic State Broadcasting Company as a reporter. Guðni has written numerous books on modern Icelandic history, including works about the Cod Wars, the Icelandic presidency, the late Prime Minister Gunnar Thoroddsen, a book about spying in Iceland, a book about former President Kristján Eldjárn, and a book about the 2008 banking collapse. He has also written dozens of scholarly articles and newspaper articles. He has received a variety of recognitions for his works.