At the age of 18, inspired by an argument with his Father over the family shoe store's window display, Jean-Claude started a Business creating billboards along French roadways. In 1963, legislation in France placed restrictions on billboard use which forced Decaux out of Business. He founded JCDecaux in 1964. He made a deal with the city of Lyons, proposing that he would build bus shelters and keep them clean in exchange for advertising space there. The company quickly expanded to other cities.
In 1980, Decaux personally designed the Sanisette public toilet, a self-cleaning public toilet, as a replacement for the pissoirs of Paris.
In January 2015, according to Forbes, he had a net worth of $6.2 billion.