Guðrún Helgadóttir was born in Hafnarfjördur on September 7th, 1935 and grew up there as one of many siblings. She worked as a secretary at Reykjavík Higher Secondary Grammar School 1957-1970 and as department manager at the National Health and Insurance Office 1973-1980. Guðrún represented the People's Alliance on Reykjavík City Council 1978-1982 and was a member of the Icelandic legislative assembly 1979-1995. She was Speaker of the Althing 1988-1991, the first woman to hold that position.
Guðrún's first book, Jón Oddur og Jón Bjarni (Jón Oddur and Jón Bjarni), appeared in 1974 and is the first of three about these scheming twin brothers. All have been republished numerous times and a film based on the stories was released in 1981. Helgadóttir is one of the best known writers of children's fiction in Iceland and her books have been translated into several languages. She received the Nordic Children's Book Prize in 1992 for her book Undan Illgresinu (From Beneath the Weeds), was nominated for the H. C. Andersen Award in 1988 and has also received various awards and recognitions for her work in Iceland. In 2005 she was awarded the Jónas Hallgrímsson Award for her contribution to the Icelandic language.
Guðrún Helgadóttir mainly writes for 7 - 13 year old readers, but has also published a few illustrated books for young children with illustrations by known artists as well as a television play and a novel for adults. Her children's play Óvitar (Infants) opened in the National Theatre of Iceland in 1979 and has also been staged in the Faeroes and in Norway.
Guðrún Helgadóttir lives in Reykjavík.