Mtagwa began his professional career on February 10, 1997, gaining a points victory over Alfred Mgaromba in Dar es Salaam.

Mtagwa tasted defeat for the first time when he travelled to Kenya to face Joseph Waweru, losing a six rounds points decision.

[1] On October 10, 2009 Mtagwa challenged for the WBO super bantamweight title against the undefeated Puerto Rican fighter Juan Manuel López in what was considered a fight of the year candidate.

[2] Although Lopez won the fight by a unanimous decision, he was hurt badly by Mtagwa in the later rounds and struggled to stay on his feet to hear the final bell.

Mtagwa did not perform as well as he did in his previous title challenge, he was knocked down three times before the referee called a stop to the action in round two.