Corrie Potgieter, who lives on a farm near Karino, west of Mbombela, heard his gardener, Fana Mashalela, talking to someone outside the house at about 07:30 on Thursday morning.
He peeped out the bedroom window and saw two men standing with Mashalela. He went to fetch his shotgun from the safe and walked to the bedroom window.
The men were gone but he became suspicious when he saw Mashalela on his knees on the veranda.
The next moment one of the robbers jumped up from underneath the window sill and pointed a pistol at Potgieter.
Potgieter fired a shot which hit the robber in the face. He died on the scene.
When police arrived, they found a plastic pistol (BB gun) next to his body.
Police spokesperson Sergeant Gerald Sedibe said Mashalela had told him there were three would-be robbers. The other two had run away.
The attack was one of several armed incidents on smallholdings around Mbombela over the past few weeks.
The areas hit the worst were Karino, Hermansburg, Cairn, Cromdale, The Rest and Alkmaar, said Vernon Lancaster of Hi Tech Security in Mbombela.