The move to lower the threshold would affect only a minority of families, with 97.6 percent of French children already enrolled at school at age three, education ministry figures show.
But Macron stressed that the change was intended to fight inequality in overseas territories and the poorest areas of mainland France in particular, where more parents opt not to send their children to school.
"I hope that with this obligation, from the start of the school year in 2019, we can correct this unacceptable differential," he told a conference organised to discuss pre-school education.
He promised that pre-school "is and will be more in the future a founding moment in the French education system".
Macron, who has named education as one of the priorities of his term, has appointed neuropsychiatrist Boris Cyrulnik to help shape changes to the pre-school curriculum in conjunction with education minister Jean-Michel Blanquer.
- with AFP