Born on December 24, 1978, in Reykjavík, Einar grew up in Kópavogur, the son of Soffía Ingibjörg Guðmundsdóttir, a project manager at Landspítali Hospital, and Þorsteinn Einarsson, a former HR manager. Einar studied at Reykjavík Junior College and earned an MPA in political science and public administration from the University of Iceland, with exchange studies at the University of Miami. During university, he chaired Politica, the political science student association, and served on the board of Vaka.
Einar joined RÚV in 2004, where he worked as a sports journalist, news reporter, presenter, and program director for “Kastljós.” He also led various elections coverage. In early 2022, he left RÚV to join the Progressive Party, leading their successful campaign in the March 2022 municipal elections, which secured four City Council seats.
Einar lives with his family in Reykjavík's Seljahverfi neighborhood. He is married to Milla Ósk Magnúsdóttir, a lawyer and assistant to the Minister of Health. He has two daughters, Auður Berta and Soffía Kristín, from a previous relationship, and a son, Emil Magnús, with Milla.