Masuku becomes Celtic's first signing of the January transfer window and the player has signed a two-year deal with the club.
The Free State outfit confirmed that the former Orlando Pirates attacker will start training with the team on Wednesday.
The club tweeted: "Bloemfontein Celtic is proud to announce the signing of midfielder, Menzi Masuku on a 2 & half year contract. The player will start training with the rest of the team tomorrow (Wednesday). #SiweleleSaMasele."
Masuku made eight appearances for the Chilli Boys in the first half of the season, although he did not find the back of the net.