His ministry began with a twenty-year academic career, but when charged with responsibility for the Sao Paulo Archdiocese he proved a relentless opponent of Brazil's military dictatorship and its use of torture as well as an advocate for the poor and a vocal defender of liberation theology.

In his later years he openly criticized the way Pope John Paul II governed the Catholic Church through the Roman Curia and questioned his teaching on priestly celibacy and other issues.

One of his sisters, Zilda Arns Neumann, a pediatrician who founded the Brazilian bishops' children's commission, was killed in the 2010 Haiti earthquake.

Then he attended the Sorbonne in Paris studying literature, Latin, Greek, Syriac at the Ecole Pratique des Hautes Etudes, and ancient history.

Arns later returned to the Sorbonne to study for a Doctor of Letters which he obtained in 1950, writing a dissertation titled "La technique du livre d'après Saint Jérome".

[4] He remained Archbishop of São Paulo for 28 years and managed an expansion of the church's presence and outreach by creating 43 parishes and more than 1,200 community centers.

He praised Cuba's record on social justice and wrote that "Christian faith discovers in the achievements of the revolution signs of the kingdom of God.... You are present daily in my prayers, and I ask the Father that he always concede you the grace of guiding the destinies of your country."

Political and theological conservatives, including Cardinal Eugenio Sales of Rio de Janeiro, protested what they interpreted as support for Castro's continued rule.

Leonardo Boff, the foremost figure in the liberation theology movement, defended Arns, saying: "Cuba carried out a revolution against hunger by ending prostitution, illiteracy and misery.

It would have established subordinate dioceses under independent bishops who would share financial and institutional resources and a common pastoral plan with each other and the archdiocese.

It was our wish that a different way of dealing with pastoral activities in the metropolitan regions be adopted, but the Roman Curia, treating this just as any other matter, paid no heed for it.

"[11] In 1968, attending the Conference of Latin American Bishops in Medellín, Colombia, he endorsed the fundamental principle of liberation theology, the "preferential option for the poor".

[12] In 1984, he joined other Brazilian prelates in Rome when theologian Leonardo Boff, the foremost figure in the liberation theology movement and a former student of Arns, was examined by Cardinal Joseph Ratzinger (later Pope Benedict XVI), head of the Congregation for the Doctrine of the Faith.

[15] Later meetings between Brazil's senior prelates, including Arns, and Pope John Paul II, cooled the conflict to a degree, and in 1986 Arns offered a conciliatory statement that he agreed with the Pope's admonition against priests taking part in politics directly, but he defended the church's advocacy on behalf of such powerless groups as peasants and native peoples, workers and inhabitants of urban slums.

[citation needed] Arns always encouraged the development of the base community movement that derived from commitment to a preferential option for the oppressed and the poor.

He encouraged religious orders in São Paulo to transfer their energies from middle class schools and hospitals in central areas of the city to the millions of marginalised people living on the periphery.

Not long after Arns became Archbishop, police raided the home of a young priest and arrested him for organizing a campaign for increased wages for workers.

[22][23] In 1975 the regime's censors at times restricted Arns's ability to protest by refusing permission to print his views in the archdiocesan weekly newspaper, O São Paulo.

A message the next week read in all the churches of the archdiocese said: "It is not lawful during interrogation of suspects to use methods of physical, psychological or moral torture, above all when taken to the limits of mutilation and even to death, as has been happening.

After retiring as archbishop, Arns held the UNESCO Chair for Peace Education, Human Rights, Democracy and Tolerance at the State University of São Paulo.

[6] Pope Benedict's meeting with Arns during his visit to Brazil in 2007 was viewed as a moment of reconciliation after their earlier dispute about liberation theology.

[31][c] For several years before his death, Arns withdrew from public life and lived in a retreat house in Taboão da Serra on the outskirts of São Paulo.