Enduring War, which opens tomorrow at the British Library, London, includes a letter from the Sherlock Holmes author to his mother about his son, who was fighting on the Western Front.
In it, the Edinburgh-born writer says: "I do not fear death for the boy for since I became a convinced spiritualist death became rather an unnecessary thing, but I fear pain and mutilation very greatly."
Conan Doyle was one of the country's most famous believers in spiritualism, which enjoyed an upsurge in popularity during the war. His son Kingsley survived the Western Front only to die of influenza in 1918.
The author later claimed publically he could converse with the spirits of the dead and began writing books on spiritualism
The exhibition, which runs until October 12, also includes manuscripts by war poets and magazines produced by troops.
Also on show are knitting patterns for the Home Front and a handkerchief with the lyrics to It's A Long Way To Tipperary, as well as manuscripts of Wilfred Owen's Anthem For Doomed Youth, Vaughan Williams' A Pastoral Symphony and Laurence Binyon's For The Fallen.
Co-curator Matthew Shaw said: "It has been a privilege to make this selection of First World War material from the library's great collections"