The change announced Thursday was "important" but should not come as a surprise, Vatican spokesman Greg Burke told CNN.
"It was expected for a long time, starting with John Paul II," he said. "He had a document, 'The Gospel of Life,' in which he said it is essentially the conditions (that) were once considered OK for allowing the death penalty have basically disappeared.
"The key point here is really human dignity," Burke said. "The Pope is saying that no matter how grievous the crime, someone never loses his or her human dignity.
"One of the rationales for the death penalty in Catholic teachings historically was to protect society. Obviously, the state still has that obligation," he said. "That is not being taken away here, but they can do that in other ways."
Francis in a 2015 speech to the US Congress said that human life must be defended "at every stage of its development."
"This conviction has led me, from the beginning of my ministry, to advocate at different levels for the global abolition of the death penalty," Francis told top US elected lawmakers.
"I am convinced that this way is the best, since every life is sacred, every human person is endowed with an inalienable dignity, and society can only benefit from the rehabilitation of those convicted of crimes."
Francis also noted that the US Conference of Catholic Bishops, a powerful lobbying force, had already advocated for the abolition of the death penalty.
"Not only do I support them, but I also offer encouragement to all those who are convinced that a just and necessary punishment must never exclude the dimension of hope and the goal of rehabilitation," Francis said.
