Judge Jerome Mnguni found Private Paul Jeke, 40, guilty of the murder of Sibekezelo Ndlovu.
In 2010 Ndlovu and Mthokozisi Manganyela were driving in Zululand, northern KwaZulu-Natal, when they saw a roadblock and sped away.
Jeke's colleague, police constable Morne Croeser, 35, shot at the car.
The car stopped and as the two men were getting out of the car, Croeser allegedly told Jeke to shoot at the two.
Jeke shot Ndlovu in the neck.
Croeser was convicted of assault for kicking and hitting Manganyela.
The men would be sentenced on Friday.