Johnson had been without a job since Platinum Stars decided against renewing his contract at the end of June 2017.
Usuthu took to their social media platforms to announce his arrival, less than two weeks before the start of the new campaign.
The Durban-based outfit will announce Johnson's assistant by the end of the week.
Former Platinum Stars and Supersport United Coach, Cavin Johnson has been appointed as AmaZulu Head Coach with immediate effect.— AmaZulu FC (@AmaZuluFootball) August 8, 2017
At the same time, Usuthu confirmed that they have parted ways with Joey Antipas and his assistant Prince Matore.
General manager Lunga Sokhela thanked Antipas and Matore for their contribution to the club and wished them well.
“We’d like to wish Mr Antipas and Matore the best of luck in their future endeavors. We thank them for their time spent with us,” Sokhela told the AmaZulu website.