Sifiso Khumalo, 31, pleaded guilty to the murders of Bheki Chiliza and Dumisani Malunga in the Ramsgate Regional Court yesterday.
"Khumalo is the local branch chairperson of the ANCYL in Port Shepstone," regional secretary Mzwandile Mkhwanazi said.
Khumalo's co-accused Samuel Cele, 34, pleaded not guilty and would appear in court again on September 19.
The two were arrested on Monday for allegedly killing Malunga, 42, and Chiliza, 39, on Sunday.
Chiliza was Port Shepstone ANC branch secretary and local National Union of Metalworkers of SA chairman. Malunga was local ANC chairman.
Numsa in KwaZulu-Natal welcomed Khumalo's guilty plea.
"What transpired in court this morning has vindicated our long-held suspicion that the cold-blooded murders were politically motivated and well-orchestrated from within," union spokesman Mbuso Ngubane said.
He said the murders were triggered by squabbles over positions of power and government perks.