Last season, Check N'Doye was Angers' captain and he reached the French Cup final with his former club, where they were beaten by Paris Saint-Germain.
His contract at the French side had not been extended, so Birmingham boss convinced him to join Birmingham.
After completing his medical on Thursday, the Senegalese midfielder played with his new team-mates at their training camp in Austria.
N'Doye is Birmingham's fourth summer signing, as they already signed David Stockdale, Marc Roberts and Craig Gardner.
He began his career with French side Epinal and he has scored 15 times for his country.