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 neighborhood.
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.
'We wanted to return it when there is peace'
Gish Amit, a 40-year-old Israeli, was looking for a PhD research topic at the National Library when he came across the collection, which includes religious books, personal writings, textbooks and poetry.
"What I found out was that around 30,000 books were taken from Palestinians, mostly from private homes," he told AFP.
"They took every book that was found, then they started to catalogue. The whole process took something like 10 to 15 years."
Uri Palit, an elderly Israeli whose Jerusalem home is furnished with ornate furniture imported from Syria, became involved in the cataloguing process in 1963 after studying for a degree in Middle East studies with Arabic and Turkish.
"My dream was that by the time I would have finished studying, there would be peace between Israel and the Arab states so I'd be of service to (diplomatic) relations," he said.
"But my hope was not realized."
Instead, he took a job in the Oriental section of the National Library.
He worked there for around a decade, recalling the special serial numbers and cataloguing process which he says showed the library always intended to preserve the books for eventual return to their owners.
"We wrote the name of the owner in pencil on the books... because we wanted to return it someday when there is peace," Palit told AFP.
"It was not a secret," he said. "Everybody knew about it."
Amit, who is writing a book on the subject, says documents including letters from the then-library director show that Israeli researchers "considered these books to be very valuable, and they really wanted them."
"They said we are saving these books, but at the same time they said we want these books, we need these books, we will look after them better than the Palestinians... so it has a lot to do with colonial attitudes," he said.
He acknowledges that the library catalogued the books carefully and kept them separate from the general collection, but questions why no efforts were made to return them.
"War is an ugly thing, but what's important is what happened in the decades afterwards," he said.
"The worst thing is the library's refusal to acknowledge the injustice that was done to the Palestinians.
"When I talked to the librarians there, they kept telling me that this was an act of rescue, even today. This I cannot accept."
And he says the library refused to cooperate when Arab-Israeli parliamentarian Jamal Zahalka requested that Sakakini's books be handed to the Sakakini Cultural Centre in Ramallah.
"They said they couldn't do anything unless Zahalka would provide them with a complete list of Sakakini's books," Amit said.
"This is ridiculous. The librarians are the only ones who can look through the books and make this kind of list."
Twinge of sympathy
In a statement to AFP, the Justice Ministry, which includes the public trustee officially responsible for the books, said the collection was considered "abandoned property."
"The law has clauses that regularize the issue of releasing the assets, according to which an asset or its equivalent can be released to the original owner who proves their ownership," it said.
Rasha questions why the burden of proof is on the owners and their heirs.
"They could contact the people who own them ... They could return them -- but they haven't done."
As a West Bank resident, she thinks it unlikely she would be able to get her grandfather's books back.
"I need a permit to even go to the library, I don't believe they would do anything to help me," she said.
Palit, who spent his entire career at the library after "falling in love" with books, rejects claims that the books were effectively stolen.
"It's their narrative, but it's not true," he said.
"They had abandoned their houses, their whole villages."
But as a book-lover, he acknowledges a twinge of sympathy at the thought of Palestinians mourning their lost libraries.
"When I read Sakakini I was sad, because I'm also bound to my books, it's an intimate relationship with books that I have," he said.
"So I felt empathy," he added, with a sigh.
"But we couldn't act otherwise."