The baboon was killed after it managed to climb over the perimeter fence at Knowsley Safari Park in Merseyside.
The adult male was forced out of its enclosure by a group of other males as it tried to protect its mate.
In a statement the safari park said: “At 8.20am on Sunday morning, the animal emergency procedure was activated after an adult male baboon was chased out of the enclosure by more than 20 other males.
“The baboon tried to protect his only female from being abducted by antagonist males - a common occurrence in baboon society. Cornered, he saw the outside of the enclosure as his safe way out and decided to face the electric fence to protect himself.
“The emergency procedures were immediately instigated, aiming to retrieve the baboon to a safe area. The police and the game keeper of the estate were contacted to assist.
“The baboon was located just outside the perimeter fence of the park. Sadly, in this situation, the safety measurement requires the animal to be shot. The estate’s game keeper took the appropriate action.”
The statement continued: “The team at Knowsley Safari care for every animal housed at the park.
“It’s very sad when something like this happens, but the police, game keeper and animal management team did everything they could to resolve the situation quickly, safely and humanely.”
The statement concluded: “The team tracked the baboon for almost two hours within the walls of the Knowsley estate. When it left the estate, at approx 10.15am, swift action was taken by the estates manager and the baboon was shot.”