Unknown to him, as the battle over the creation of the Jewish state raged, teams of Israeli librarians and soldiers were collecting tens of thousands of books from Palestinian homes in Jerusalem, Haifa, Jaffa and elsewhere -- including 256 from Barghouti's home in the Katamon neighbourhood.
For Israel, the effort was a way to preserve books which would eventually be returned to their owners. But for the Palestinians, it was theft.
Omar's granddaughter Rasha Barghouti remembers his stories about his books.
"He was a lawyer who had an office on Jaffa Street," she told AFP.
"He used to write a lot -- his diaries, the history of Palestine, of Palestinian families, the Jordanian regime, the tribal law."
After two years in exile in Egypt, Barghouti moved to the West Bank city of Ramallah, reaching out to Jewish friends in what was now Israel to try and get his books back.
"He explained when you lose your furniture, household items, you can replace them. But with his books, it was really as if he lost the woman he loved most in his life," she said.
His experience mirrored that of other Palestinians who lost their book collections, including intellectual Khalil Sakakini, who wrote longingly about his books from exile in Egypt.
The Barghouti family tried for years without success to locate the books, but until 2012, Rasha had no idea that they were most likely held in a basement in Israel's National Library.
There they are part of a collection of around 30,000 books, marked "AP" -- "abandoned property" -- and accessible only by special request.