Ntsundwana turned out for the Wits Multichoice Diski Challenge side last season, and had a brief training spell with the first team.
The 20-year-old's contract with the Clever Boys has since expired, with Usuthu having leaped at the opportunity to snap him up ahead of their return to the PSL this season.
"AmaZulu have signed him [Ntsundwana] and it is an outright deal," a source told this website.
When contacted for confirmation, AmaZulu general manager Luga Sokhela confirmed the signing but was unable to give further comment.
The towering frontman is now the Durban-based outfit's fifth striker in their ranks, joining the likes of Siyabonga Nomvete, Mabhudi Khenyeza, Mhlengi Cele and Siyethemba Mnguni, who can also play an attacking midfield role.
Ntsundwana featured in the inaugural Prince Mangosuthu Legacy Cup at Ulundi Stadium this past weekend, as Joey Antipas' side lost 1-0 in the final to Bloemfontein Celtic on Sunday.