Pope Leo spoke out in defense of the poor and pensioners in Argentina during a visit that is the first by a pontiff to the country in nearly four decades.
The visit is also the first by a pontiff to the home country of the late Pope Francis in nearly four decades.
Milei came to office on a promise to revive Argentina's ailing economy and tame runaway inflation by shrinking the welfare state.
He was met with calls to help mend deep divisions after three years of austerity under Milei.
His government has targeted public hospitals, universities and pensioners in particular.
Leo made the journey just three weeks after undergoing surgery for lung cancer.
Argentines are hoping the leader of the world's 1.4 billion Catholics will help unite the country.
He is on an ambitious 12-day tour of the continent where he served nearly two decades as a missionary.