De Greiff was assistant professor of philosophy in the State University of New York from 1992 to 2002, and associate professor there in 2000-2003. He was a Laurance S. Rockefeller Visiting Faculty Fellow at the Center for Human Values, Princeton University, in 2000-2001. In 2001 he joined the International Center for Transitional Justice (ICTJ), a human rights INGO based in New York City, becoming its director of research.
While at the ICTJ de Greiff provided advice on transitional justice to the World Bank, other UN agencies, governments, truth and reconciliation commissions and other bodies, including the National Reparations Commission (Comisión Nacional de Resarcimiento) in Guatemala, the Colombian National Commission for Reparation and Reconciliation (Comisión Nacional de Reparación y Reconciliación), the Equity and Reconciliation Commission in Morocco and the Truth and Reconciliation Commission (Peru). He has also worked in the Philippines and Palestine, and has prepared for the UN Office of the High Commissioner for Human Rights (OHCHR) Rule of Law Tools for Post-Conflict States on Reparations Programmes, as well as advising OHCHR projects on reparations, Disarmament, Demobilization and Reintegration, and economic, social and cultural rights in post-conflict situations.
In 2011 the UN Human Rights Council established a mandate for a Special Rapporteur on the promotion of truth, justice, reparation and guarantee of non-recurrence. De Greiff was one of 15 applicants for the three-year part-time post, and was one of three shortlisted. De Greiff's selection was announced at the conclusion of the 19th HRC session on 23 March 2012.
De Greiff has lectured at Yale, Harvard, Columbia, Cornell, NYU, the European University Institute and other universities across Europe and Latin America. He has edited 10 books on justice and human rights and many articles on transitions to democracy, democratic theory, and the relationship between morality, politics, and law. A member of the board of editors of the International Journal of Transitional Justice, he holds dual Colombian and US citizenship.