In his memoir Paris ma grand'ville, Grenier describes being briefly arrested and narrowly avoiding execution by the Occupation forces on the boulevard Saint-Germain.

He left professional journalism in 1964 to assume a position on the editorial board of the prominent French publishing house Gallimard.

In addition to working as a radio host and a writer for television and cinema, he was a member of the board at Gallimard from 1964 up until his death.

He is best known in the United States for his work The Difficulty of Being a Dog (Les larmes d'Ulysse), translated by Alice Kaplan.

Until his death, he was writing and a busy conference attendee, speaking about his works, literature, Gallimard, or his friends: Albert Camus, and Brassaï.