After obtaining his baccalaureate in philosophy in 1946 in Phnom Penh, Vannsak continued his studies in Paris on a scholarship and worked as a Khmer-language assistant at the National School of Modern Eastern Languages (Ecole nationale des Langues Orientales).

She held diplomas in the Cambodian, Lao, and Thai languages, and also obtained a degree in physical science at the University of Caen, as revealed by the (unpublished) writing of Khing Hoc Dy, a former student as well as friend of Keng Vannsak.

[8] In 1952, he returned to Cambodia with his wife and a bachelor's degree which he obtained at the Faculty of Literature and Human Science University of Paris in 1951.

Ieng Sary, a former high school classmate who later became Minister of Foreign Affairs of the Khmer Rouge government himself told me later: 'You are too sensitive.

Strongly opposed to the Cambodian monarchy, Vannsak was also known for his role as a mentor to Saloth Sar, later known as Pol Pot, who ruled Cambodia from 1975 to 1979.

As described by historian Philip Short in his book titled "Pol Pot – Anatomy of a Nightmare", during the winter of 1950, more exclusive student meetings took place several times every month at Keng Vannsak's flat in Paris “to discuss political issues and more precisely about the future of Cambodia, a country which, for the first time, was directly affected by the war in Vietnam”.

[10] Philip Short also details that at that time communism was not their main concern, and recalls that Vannsak himself was more aware of political reality than most of his fellow-students.

Vannsak appeared to offend a young Frenchwoman of the high bourgeoisie by offering her, a year before, to go and spend the afternoon at the Fête de l'Humanité, organised by the French Communist Party.

Before his death, Vannsak wrote a letter to Premier Hun Sen to let him know that he wanted to visit Cambodia after many years spent abroad since the 1970s.