And Monaco vice-president Vadim Vasilyev said in a statement that the arrival of Antonucci is part of the club's planning for the future.
"We are very satisfied with the arrival of Franco Antonucci, who is part of our strategy to attract Monaco of promising young players," the official said.
"At Ajax, Franco Antonucci showed a lot of qualities, which led him to be followed by the biggest clubs. We believe very much in him.
"Our structures have made it possible to reveal many players and we are convinced that they will help Franco to express its potential at the highest level in the near future."
Antonucci added: "I am very happy to get involved with AS Monaco, a prestigious club that is one of the top European clubs, with a very attractive project.
"I plan to work very hard to flourish with this jersey."