The Toulouse player has made 82 appearances for his current club, but has decided to join the Ligue 1 title challengers until the end of the season.
The agreement includes an option for a permanent move in the summer.
Speaking about his transfer, Abdennour was full of praise for his new teammates and said that he was ready to commit to Claudio Ranieri's project.
"I am very proud, AS Monaco FC is a great club, very professional, with excellent staff, great players and great ambition," he told the club's official website.
"I am ready to help my teammates. I will do everything to succeed. We have a special purpose."
Monaco are second in the league, six points behind Paris Saint-Germain.