The Open Society Foundations (OSF) announced in May that it was leaving Hungary, citing what it called the "repressive" policies of nationalist firebrand Prime Minister Viktor Orban.
"There are still some colleagues working here in the office, but we will have closed for good by 31 August," the OSF spokesman in Budapest Daniel Makonnen told AFP.
In an interview with the 168ora weekly, the head of OSF operations in Hungary, Katalin Koncz E., said she felt bad about the move.
"I have to put an end to 25 years' work and watch as an institution I've spent my life building becomes a desert -- everyone is clearing away their things and my colleagues are disappearing."
She indicated that she herself would stay in Budapest, adding: "I take comfort in knowing that a brilliant office and great conditions are awaiting my friends in Berlin, where they will be able to take up the work with fresh energy."
In April, Orban won a landslide victory in an election that handed him a third straight term as prime minister, and he has since indicated he wants to use this mandate to intensify his anti-migrant, nationalist and culturally conservative agenda.
Anti-immigrant rhetoric was a key part of Orban's election campaign and his government accuses Soros of using his organisations to orchestrate immigration and undermine the cultural and religious identity of Europe. Soros denies this.
In June, Hungary passed the controversial "Stop Soros" law, which includes a punishment of up to a year in prison for anyone assisting someone who enters the country illegally.