Lagercrantz was born in Stockholm, Sweden, the son of bank director Carl Lagercrantz and Countess Agnes Hamilton. He married Martina Ruin (born 1921), daughter of Professor Hans Ruin and Karin Sievers, in 1939. Lagercrantz is the father of actress Marika Lagercrantz and author David Lagercrantz. His sister Lis Asklund was an author, social worker, curator, and program producer for Sveriges Radio. His nephews Lars Lönnroth and Johan Lönnroth are also famous in their own right.
Lagercrantz commanded considerable influence as a critic and publicist. He became an expert of sorts in literary biography, and several of his studies on important Swedish writers are still cornerstones of Swedish literary studies, in particular, his biography of August Strindberg (1979) and his portrait of his friend Gunnar Ekelöf, Jag bor i en annan värld men du bor ju i samma.
During the latter part of his professional life, Lagercrantz' concerns in his role as literary critic and cultural pundit progressed from the strictly aesthetic to the political. In 1958, he published a biography of the late poet Stig Dagerman which was severely criticized by a young Beppe Wolgers for being confined to Dagerman's "dark predicament" and not completely representing a man "who paid such great interest to cinema as well as football". Lagercrantz' political engagement became apparent during his time at Dagens Nyheter, where he was head of the cultural section from 1951 and editor-in-chief from 1960 on. He was an influential, albeit controversial, voice in the political and cultural radicalism of the 1960s and 1970s, assuming a crucial role in the national secularization debate.
Lagercrantz in his public role gave rise to strong emotions. His cultural radicalism in particular was perceived as provocative in light of his aristocratic background (his mother belonged to the noble Hamilton family). Lagercrantz was widely criticized for the conciliatory and fairly positive appraisals of Communism that he published in Dagens Nyheter after travelling as a journalist to the Soviet Union and China.
Lagercrantz dwelt on parts of this in his autobiographical works. His upper-class childhood and adolescence are the subject of Min första krets (1982), and the turbulence of his time at Dagens Nyheter is the topic of his memoir Ett år på sextiotalet (1990).
Olof Lagercrantz grew up in Falköping and in 2001 was awarded the title of Honorary Resident of Skaraborg by the Skaraborg Academy in tribute to the fact he had wielded one of the mightiest pens of the 20th century.
- Den döda fågeln ("The Dead Bird", 1935, poems)
- Den enda sommaren ("The Only Summer", 1937, poems)
- Jungfrun och demonerna ("The Maiden and the Demons", 1938, a study of Erik Axel Karlfeldt)
- Trudi (1939, novel)
- Möten med bibeln ("Facing the Bible", 1941)
- Dikter från mossen ("Poems from the Bog", 1943)
- Om kärlek ("On Love", 1946)
- Fågelropet ur dimman ("The Bird's Call Out of the Fog", 1947, essays)
- Studieplan i svensk lyrik ("Syllabus of Swedish Lyric Poetry", 1950)
- Agnes von Krusenstierna (1951, revised 1980, literary study)
- Dagbok ("Diary", 1954)
- Dikter och dagbok ("Poems and Diary", 1955)
- Stig Dagerman (1958, literary study)
- Ensamheter i öst och väst ("Solitudes in the East and the West", 1961, travel literature)
- Svenska lyriker ("Swedish Lyric Poets", 1961)
- Linjer ("Lines", 1962, poems)
- Från helvetet till paradiset ("From Hell to Paradise", 1964, a study of Dante)
- Dikter 1935-1962 ("Poems 1935–1962", 1964)
- Den pågående skapelsen ("The Creation in Progress", 1966, a study of Nelly Sachs)
- Opinionslägen ("Current Opinions", 1968)
- Att finnas till ("To Exist", 1970, a study of James Joyce)
- Tröst för min älskling ("Comfort for My Beloved", 1971)
- Tretton lyriker och Fågeltruppen ("Thirteen Lyric Poets and the Troop of Birds", 1973)
- Enhörningen ("The Unicorn", 1977, prose)
- Från Aeneas till Ahlin ("From Aeneas to Ahlin", 1978)
- August Strindberg (1979, literary study)
- Eftertankar om Strindberg ("Second Thoughts on Strindberg", 1980)
- Min första krets ("My First Circle", 1982, autobiography)
- Om konsten att läsa och skriva ("On the Art of Reading and Writing", 1985, essay)
- Färd med mörkrets hjärta ("A Journey with the Heart of Darkness", 1987, a study of Joseph Conrad)
- Ett år på sextiotalet ("A Year in the 60s", 1990, autobiography)
- En blödande ros ("A Bleeding Rose", 1991, selected poems)
- Att läsa Proust ("Reading Proust", 1992)
- Jag bor i en annan värld, men du bor ju i samma ("I Live in Another World, but You Live in the Same", 1994, a study of Gunnar Ekelöf)
- Mina egna ord ("My Own Words", 1994, selection of articles from Dagens Nyheter)
- Dikten om livet på den andra sidan ("The Poem of Life on the Other Side", 1996, a study of Emanuel Swedenborg)
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