He is known for the series of children's books he created with René Goscinny, Le Petit Nicolas, and also for his poster-like illustrations, usually drawn from a distant or high viewpoint depicting detailed countrysides or cities.

[2][3] He was first raised by foster parents, but then his mother took him back in; she lived with his alcoholic stepfather, and the child experienced violence at home.

[6] After lying about his age, he joined the French Army in 1950, since it was "the only place that would give me a job and a bed", he subsequently explained, and would occasionally get into trouble for drawing while he was supposed to be keeping watch during guard duty.

His "mute" watercolours or single image sketches, where the characters speak in pictures or not at all (but somehow manage to convey a rich story) slowly gained international attention.

[3] A translation of his drawings into English, by Anthea Bell, was published in four volumes in 2006: Nothing is Simple (1962), Everything is Complicated (1963), Sunny Spells (1999) and Mixed Messages (2003).

[9][3] President Emmanuel Macron wrote on Twitter : "Tender irony, the delicatesse of intelligence, the jazz: we will not be able to forget Sempé.