The 26-year-old has not played for the national side since September 2012, after saying he was frustrated with the organisation within the team and, subsequently, falling out with a number of team-mates.
Guinea coach Michel Dussuyer confirmed that it was Constant who was the driving force behind his return, citing "the long term project" of the team as the main reason for his decision.September's boycott was not the first controversy surrounding Constant and the Guinea side, however. He also sat out the 2012 African Cup of Nations in Equatorial Guinea and Gabon when he aired his grievances for the first time.
The Milan man has represented his country 18 times since his debut in 2007, scoring twice.
Last month, the 26-year-old walked off the pitch during a friendly for Milan against Sassuolo, after being subjected to racist abuse by the opposing fans.