He was best known for his documentation of the genocide which occurred under the Khmer Rouge (KR), and for being one of the first people to expose the human rights abuses being carried out at the time.

[9] After expulsion, Ponchaud collected hundreds of written and oral accounts from refugees along the border with Thailand and in France.

[4] Following the KR victory, all contact with the outside world was shut down, but following an editorial in Le Monde in February 1976, Ponchaud wrote a three-page article, which described the systematic abuses he had witnessed while Phnom Penh was being emptied,[10] and following this he wrote Cambodge année zéro (Cambodia: Year Zero), a book on the Cambodian genocide, which was published in 1977, and his book is credited with being one of the first publications which dealt with the genocide.

[12] For four years after his expulsion, he and François Bizot helped Cambodian and French citizens escape from Cambodia.

[4][17] Ponchaud said of the genocide that it, "Was above all, the translation into action the particular vision of a man [sic]: A person who has been spoiled by a corrupt regime cannot be reformed, he must be physically eliminated from the brotherhood of the pure.