Hummes received his episcopal consecration on the following 25 May from Archbishop Aloísio Lorscheider, OFM, with Bishops Mauro Morelli and Urbano Allgayer serving as co-consecrators.

It was here that he began his support for liberation theology, and forged his friendship with the union boss at the time, Luiz Inácio Lula da Silva.

Hummes was created Cardinal-Priest of S. Antonio da Padova in Via Merulana by Pope John Paul II in the consistory of 21 February 2001.

[9][10] A year later, Hummes was appointed honorary president of the Pan-Amazonian Ecclesial Network (REPAM), established in 2014 in Brasilia, Brazil, during a meeting of bishops whose territories include Amazon regions, priests, missionaries of congregations who work in the Amazon jungle, and national representatives of Caritas and laypeople belonging to various Church bodies.

In his message, he reiterated that the creation of the Pan-Amazon Ecclesial Network "represents a new incentive and relaunch of the work of the Church in Amazonia, strongly desired by the Holy Father.

[13] On 29 November 2015, ahead of the 2015 United Nations Climate Change Conference Cardinal Hummes appeared again on the world's global media stage when he and Avaaz campaigner Oscar Soria displayed a pair of shoes donated by Pope Francis to support a climate demonstration in Paris that had replaced a planned march after French authorities had banned public protests in the aftermath of the November 2015 Paris attacks.

Parisians and others from around the world donated shoes and set them up at Place de la Republique, in a symbolic march organized by the civic movement Avaaz which gained the support of the pope.

There were lots of expectations, it was a great and symbolically strong way of pressure from the people, and as well the presence of Pope Francis, in this clamor to avert climate change".

[17] Cardinal Hummes who criticized the spread of global capitalism, claimed that privatizing state companies and lowering tariffs had contributed to "misery and poverty affecting millions around the world".