The open air Mass for the beatification of Father Jose Brochero was attended by an estimated 150,000 people in the northern city of Cordoba.
On hand were 3,000 gauchos, or Argentine cattle herders, wearing ponchos of the kind Brochero did. He was known here as the "gaucho priest."
Brochero, who died of leprosy, lived from 1840 to 1914.
Angela Amato, a cardinal representing Pope Francis, who is Argentine, oversaw the Mass.
Beatification is the last step before canonization, or sainthood.
"This shepherd who smelled of sheep became poor among the poor," the pope said in a letter read out at the Mass.
It was the first beatification in South America under Francis, who was elected pope in March of this year when Benedict XVI resigned.