Cardinal Vincent Nichols was addressing a Special Conference held at the United Nations on the combatting of human trafficking and modern slavery.
He said: "Human trafficking and slavery radically strips a person of this fundamental dignity, reducing them to the status of a commodity.
"It is an evil crying out to heaven. That there are over 20 million people callously held in modern slavery in our world today is a mark of deep shame on the face of our human family that no words alone can remove.
"The challenge that the eyes of faith see before us today is to work to our utmost to rescue, protect, assist and serve the poorest of the Father's children who have be sold into slavery even as Joseph was sold into slavery by his brothers 'in the beginning'(Gen 37.32)."
The cardinal listed three moments in his life that had made him interested in the issue.
"The first was four years ago when I listened, for the first time, to the witness of a young woman who had been betrayed into the slavery of enforced prostitution. Her story was heart-wrenching," he said.
The second was watching how the Metropolitan Police had created links with religious woman fighting the crime.
He added: "The third moment came two years ago when, at the end of our first Santa Marta Conference in Rome, Pope Francis turned to me and asked me to keep this work going. That is an order that cannot be refused!"
The Santa Marta Group brings together the leaders of law enforcement agencies from several countries with the Catholic Church to fight human trafficking.