19-year-old France U-21 international Jean joins from Troyes on a five-year deal but will be loaned back to his former club for the forthcoming season.
The teenager starred in his club’s promotion campaign last season, hitting 10 goals in 28 games as Troyes claimed the Ligue 2 title by 13 points.
37-year-old Ricardo Carvalho, meanwhile, will be available after extending his contract with the club until June 2016.
“I am very happy to continue my adventure with Monaco. I feel very good at the club and with my team-mates and all the staff,” the former Chelsea and Porto defender told the club website.
“For two years, we have had very good results and we will do everything to continue this way.”
Carvalho, who arrived from Chelsea in 2013, made 25 starts for the club last season as they finished third in Ligue 1, sealing qualification for the Champions League.