Irish Catholics were much less devout before the famine, according to a new documentary.
The RTE programme, Rome v Republic, examines how the church seized such a strong hold over every aspect of the nation's life after the foundation of the State.
It reveals that the famine unexpectedly strengthened the influence of the Catholic Church in Ireland.
The documentary, presented by former justice minister Michael McDowell, found Irish people in the late 1700s and early 1800s had a much laxer attitude toward mass-going.
"We know people wouldn't have gone to mass every Sunday, but this is not to say they weren't religious in their own way," said Dr Sarah Roddy, from the University of Manchester.
"But I suppose the church might have seen it as a kind of unorthodox religion, which combined going to mass every now and then but also doing things which had ancient pagan roots as well."
Daniel O'Connell's campaign for Catholic emancipation energised the country's Catholics in a mass movement in the early 19th century.
However, Professor Mary Daly, from UCD, said the famine had an unexpected effect on the Catholic Church in Ireland.
The population went from just under 8.2 million in 1841 to just under 5.8 million in 1861.
Prof Daly said the dramatic population decline disaster gave the Catholic Church more control over its flock.
"The reality about religion pre-famine, it's not like the place is full of atheists, it's just that in many areas there aren't enough priests," she said.
"Basically the Catholic Church in 1841 did not have the manpower to really look after the six million-odd Catholics in Ireland at the time."
She said the deaths of millions of Catholics meant the church had smaller numbers of more God-fearing parishioners.
"A lot of the population loss occurred in the poor and very poor people who were not regular Sunday mass-goers, who would have practiced a different form of Catholicism based around a good mixture of superstition and folk belief with Catholicism. They are removed from the scene."
Prof Daly said the middle classes left behind were much more devout.
Presenter McDowell also reveals how the first Free State constitution was a very secular document but then a raft of "Catholic morally-inspired legislation" was brought in, as the new, cash-strapped Irish Republic was forced to rely on the 13,000 religious personnel across the country.
Rome v Republic is on RTE One tomorrow at 10.15pm