The 29-year-old, who played with Tapuwa Kapini in Zimbabwe's Under-20 national side, impressed Usuthu's technical less than a week after he started training with the team.
Dube spent most of his career playing in the USA, where he played for MLS side New England Revolution and prior to his move to AmaZulu, he spent six months with Chicago Fire.
The Durban side has also signed Shaun Cramer, who is a midfielder from their feeder side Durban Warriors. Cramer has also signed a three-year deal, but he will be loaned back to Warriors for a year to gain more experience.
Dube's arrival makes it five the number of new signings made by AmaZulu in preparation for the new season after they also enlisted the services of Prince Hlela, Sifiso Vilakazi and Liberian midfielder Dulee Johnson.