Dagur B. Eggertsson (born 19 June 1972) M.D. is a member of the Icelandic Parliament (MP) since 2024 and the former Mayor of Reykjavík City (2014-2024). Currently he is the chair of the Icelandic delegation to the NATO Parlimentary Assembly, vice-chair of the budget committee and has a focus on climate change, housing and international affairs in his parlimentary work. Dagur studied, trained and worked as a physician and holds a master's degree in Human Rights and International Law from the University of Lund in Sweden.

Dagur was originally elected to the Reykjavik City Council in 2002 and was the vice-chairman of the Social Democratic Alliance (2009-2013) until shortly before taking office as Mayor in 2014. Dagur has been a frequent keynote speaker and participant in international forums as mayor. During his mayorship he succeded Anne Hidalgo, Mayor of Paris, as the chair of the OECD Champion Mayors for Inclusive Growth Initiative. That is a coalition created by the OECD in recognition of the important role local leaders play in addressing inequalities within their cities.

Dagur has written four books, among them New Reykjavik, the transformation of a young city (2021). New Reykjavik highlights the development of the city, not least in the areas close to Dagur‘s heart: housing, planning, economic development, education, inequality, prevention, public health and the transformation of public space.

Dagur grew up in Reykjavík and is married to Arna Dögg Einarsdóttir, a medical doctor and chief of palliative care at Landspitalinn - The National University Hospital of Iceland. They have four children.