Goal revealed last week that a deal was on the cards for the youngster, with those at Stade Louis II prepared to invest heavily in players of huge promise.
They have now acquired a talent being tipped for the top, with Geubbels having already graced Ligue 1, become the youngest player ever to turn out in Europa League competition and figured in the Goal NxGn.
He has also impressed with French national teams at youth level and is looking forward to furthering his career with Monaco.
“The project of the club is ambitious and relies on the development of young players.
“I cannot wait to meet my new team-mates, to learn from them. I am ready and determined to help the team do great things.”
Vadim Vasilyev, Monaco’s CEO, added: “The arrival of Willem Geubbels forms part of our ambition to develop the best European talent.
“Willem has already demonstrated a lot of qualities and great potential. With patience and a lot of work, we are convinced that he will arrive at the top level.”
Geubbels had been with Lyon since the age of nine, making his senior bow in September 2017.
In gracing a meeting with Dijon, he became the first player born in the 21st century to appear in a Ligue 1 fixture.