He grew up in the Hell's Kitchen neighborhood of Manhattan, New York alongside his sister Pauline, who's also an actress. He is the son of Marc Chalamet and Nicole Flender. His grandfather is screenwriter Harold Flender, and his uncle is director Rodman Flender. In 2020, he dated actress Eiza González. He was previously romantically linked to actress Lily-Rose Depp. He became romantically linked to Kylie Jenner in 2023.