The Mayo man had been sent to the suburbs of the country's capital Lima in the early 1970s to carry the Catholic message – but very soon he began to doubt that an autocratic and secretive church, as he saw it, could do anything to help the thousands of people living in grinding poverty.
For instance, it had done nothing to help this teenage boy on a makeshift bed in a room made of bamboo and cardboard, he thought to himself as he delivered a final blessing.
The boy's fixed stare would stay with Waldron for years, he recalls in his memoir A Dawn Unforeseen. "It seemed to say, 'Padre, look at these conditions, look at what they have done to me'," he writes.
That experience and the plight of thousands living in dire conditions spurred Waldron into action. With some like-minded colleagues, he began to push for reform. Aid was no good if it just patched over the misery; it had to empower people and allow them to think for themselves, he argued.
He and other priests began to push for a new pastoral approach inspired by Liberation theology. They questioned the morals of building big churches and the ethics of playing golf with the elite. Not surprisingly, they soon came into conflict with the authorities.
The intervention, Waldron writes, was "ruthless and dictatorial". He was moved to a new parish where the church and parish house were built entirely on the city's former dump.
Metres of rubbish lay underfoot and a pervading burning smell filled the air. The whole place shook when a car passed, yet these people living in houses with cracked walls and unstable foundations had a never-say-die spirit.
Luke Waldron writes with searing honesty about how he, and hundreds of Catholic missionaries before him, had underestimated the local community. They were talented, intelligent people with a rich culture who needed education and facilities, not more churches and sacraments, he writes.
And they had their own take on Catholicism.
During a visit to a mothers' club in Lima, the Archbishop of Dublin was perturbed to find a calendar with scantily clad ladies next to a picture of the Sacred Heart. When the archbishop asked if that was appropriate, the mothers responded: "What's the problem, Padre?"
In 1971, Luke Waldron decided to leave the priesthood, but he stayed on as a social worker.
He had already met Carmen, a fellow social worker, who would become his wife and together they had three children.
He was afraid he would be seen as a 'spoiled priest' at home, but his parents in Ballyroe, Knock, Co Mayo, respected his decision.
What shook him was the "coldness and lack of humanity" from his superiors. "I was a living, walking source of grave scandal, so my future activity in the church had to be drastically curtailed."
Waldron and his new wife went on to carve out a life as community development workers and documentary-makers. He would make 40 documentaries, including one about the people who were 'disappeared' during the political violence in Peru in the 1980s. When the situation deteriorated, the family moved back to Ireland.
Now Lima is back in the news following
the arrest of an Irishwoman and her Scottish friend on suspicion of drug
smuggling, but it is much more than a drugs capital.
Waldron's memoir paints a nuanced picture of the city and its resourceful people, who have survived against the odds.
Waldron's memoir paints a nuanced picture of the city and its resourceful people, who have survived against the odds.