The hunter, 59, who has not been named, died on Sunday morning after being found unconscious near the village of Laza, in the province of Ourense in the northwestern Spanish region of Galicia.
The attack happened after the hunter shot the boar, injuring the animal who was then surrounded by his hunting dogs. When he approached the injured beast to finish it off, the boar charged and gored him in the leg.
Local police sources quoted in Europa Press called it an "unfortunate accident".
Before the hunter could stab the boar, it charged, piercing his right leg. The man managed to call emergency services for help, but was unconscious and "not breathing" by the time they arrived.
Teams from the two ambulances and the emergency helicopter that arrived on the scene shortly after midday on Sunday were unable to resuscitate the man, who was from the nearby city of Verín, where he worked as a policeman.
He died due to loss of blood from a "severe tear" in his right leg.