Guðmundsson ws born in Þverfell (Borgarfjörður). He grew up in poverty and was self-learned. In 1923 he worked as a journalist and worked then as free-lance writer in Copenhagen and Olso until 1938, when returned to Reykjavík.

In Norway Guðmundsson published in Norwegian a collection of stories, ISLANDSK KJÆRLIGHET (1924), which gained success and astonished the critics by mastery of Norwegian idiom and style. It was followed by several novels, among them the autobiographical HVITE NETTER (1934). After returning to Iceland Guðmundsson began writing in Icelandic. He died on November 20, 1983 in Reykjavík.

Guðmundsson's best-known novels are BRUDERKJOLEN (1927) and DET HELLIGE FJED (1932). He published over 30 novels, which have been translated into some 30 languages. Central themes in his works were love and passion, hate and fear - also nature played major role in Guðmundsson works.

Selected works:

• RÖKKURSÖNGVAR, 1920
• ISLANDS KJÆRLIGHET, 1926
• BRÚðARKJÓLINN - BRUDERKJOLEN, 1927
• ÁRMANN OG VILDÍS, 1928
• LIVETS MORGEN, 1929
• SIGMAR, 1930
• STRÖNDIN BLÁ - DEN BLÅ KYST, 1931
• HELGAFELL - DET HELLIGE FJED, 1932
• DEN FÖRSTE VÅR, 1933
• HVITE NETTER, 1934
• BÖRN JARðAR - JORDENS BARN,1935
• LAMPEN, 1936
• GUDINNEN OG OKSEN, 1938
• ARMA LEY, 1940
• NÁTTRÖLLI GLOTTIR, 1943
• FÉLAGI KONA, 1947
• SAGA UM SKALD, 1948
• KVÖL Í REYKJAVÍK, 1948
• LEIKMANNS Þ
ANKAR, 1949
• ÞAKAN RAUðA, 190-52
• HARMLEIKURINNA Á AUSTURBÆ, 1955
• KRISTMANNSKVER, 1955
• ISOLD HIN SVARTA, 1959
• ÆVINTYR Í HIMINGEIMNUM, 1959
• DÆGRIN BLÁ, 1960
• LOGINN HVÍTI, 1961
• VOLUSKRIN, 1961
• ISOLD HIN GULLNA, 1962
• ÁRMANN OG VILDIS, 1963
• TORGIð, 1965
• SKAMMDEGI, 1966
• BLÁBRÁ OG FLEIRI SÖGUR, 1968
• TILHUGALIF, 1968
• SMIðURINN MIKLI, 1969
• SUMAR Í SELAVÍK, 1971
• BROSIð, 1972
• LEIKAR Að LJÓðUM, 1974
• STJÖRNUSKIPIð, 1975
• SKALDEVERK, 1978
• HAUSTLJÓð, 1981