Cape Town online auction site for books, maps and documents AntiquarianAuctions.com expect it to sell for $5500 on July 16.
The eight-page letter has never been offered at auction before. At the time it was penned in 1913, Casement was a passenger on the SS Armadale Castle, returning to England after time in South Africa with his brother.
He thanks his correspondxents - a Mr and Mrs de Villiers - for their kindness in having come to see him off at Cape Town harbour before expressing concerns about British imperialism in both South Africa and Ireland.
"Equal Rights"
He writes: "I know quite well what the English mean by "Equal rights"! We've had plenty of that kind of talk in Ireland but we've never seen the real thing.
"I want Ireland to be restored to Europe. I want to see her again a country - a land, a nation, playing her part in European life and always as I believe, playing it just and rightly. I don't look upon her at all as a bit of English property, or as belonging to England, or as being "owned" by anyone but herself and her own children and I hope before I die to see something start to become reality … I only want to be "an Irishman" - to me it is the proudest title upon Earth."
Though knighted in 1911 for his role in exposing atrocities against native peoples in the Congo and Peru, Casement was later executed for treason after he sought German help for the 1916 armed uprising in Ireland.
