The hush-hush meeting, which was first revealed last week by Subang parliamentarian R Sivarasa during his debate with Perkasa information chief Ruslan Kassim, was held at the luxury Plaza Hotel in Manhattan.
The prime minister's meeting with Soros, who is accused of funding Malaysian NGOs to push for regime change, took place on Sept 27, 2010.
It is believed that at least one other top Umno leader was present at the get-together.
Najib, who became prime minister in 2009, made his maiden speech at the UN General Assembly in NY on the same day he met with the billionaire financier.
Among those who accompanied Najib on that trip were his wife RM, Foreign Minister Anifah Aman and Malaysian ambassador to the US Jamaluddin J.