Alston graduated from the University of Melbourne with an LL.B.(Hons.) in 1972 and an LL.M. in 1976 and from the University of California at Berkeley School of Law.
His brother is the former Australian federal Cabinet minister and High Commissioner to the United Kingdom, Richard Alston.
Alston's first academic appointments were at Tufts University (1985–89) and Harvard Law School (1984–89). Alston was then Professor at the Australian National University (1990–95), and also director of its Center for International and Public Law. He was then Professor at the European University Institute (1996–2001), before moving to New York University School of Law, where he is the John Norton Pomeroy Professor of Law. In 2015, it was announced that he would be a faculty instructor in the newly launched NYU Law Institute for Executive Education.
In human rights law, Alston has held a range of senior UN appointments for over two decades. From 1987 to 1991 he was the first Rapporteur for the UN Committee on Economic, Social and Cultural Rights; he then chaired the Committee from 1991 to 1998.
At the 1993 World Conference on Human Rights he was elected to chair the first meeting of the presidents and Chairs of all of the international human rights courts and committees (including the European Court of Human Rights, the Inter-American Human Rights Court, the African Commission on Human and Peoples' Rights, and the UN Human Rights Committee).
He was appointed by the United Nations Secretary-General in 1988 to suggest reforms to make the United Nations human rights treaty monitoring system more effective. His major reports in 1989, 1993, and 1997 provided the impetus for continuing efforts by the UN Office of the High Commissioner for Human Rights and the UN Human Rights Council to streamline and improve the rather unwieldy monitoring system.
His other United Nations appointments include Special Adviser to the UN High Commissioner for Human Rights on the Millennium Development Goals. He was appointed to that post by Sergio Vieira de Mello, and has continued to advise successor High Commissioners, including Louise Arbour and Navanethem Pillay.
He has been actively involved in the field of children's rights and the legal adviser to UNICEF throughout the period of the drafting of the U.N. Convention on the Rights of the Child. He participated in the UNICEF delegation to the drafting sessions of the Convention and continued to advise UNICEF for several years after the Convention's adoption in 1989, especially in relation to promoting the ratification of the Convention by countries around the world. He published two studies for UNICEF on children's rights. The first was The Best Interests of the Child: Reconciling Culture and Human Rights (1994), and the second, with John Tobin, was Laying the Foundations for Children’s Rights, published in 2005 by UNICEF.
From August 2004 – July 2010 he was the United Nations Special Rapporteur on extrajudicial, summary or arbitrary executions. In that capacity he reported to the UN Human Rights Council and the General Assembly. As Special Rapporteur, Alston visited Nigeria, Sri Lanka, The Philippines, Guatemala, Lebanon, Israel, The Central African Republic, Brazil, Afghanistan, the USA, Kenya, Ecuador, and Colombia, and issued a report in each case to the relevant government and to the United Nations.
Alston's reports to the UN relating to extrajudicial executions also dealt with broad thematic issues that arose in many countries, such as witchcraft and vigilante killings, national-level commissions of inquiry dealing with unlawful killings, the problem of prisoners running prisons, the importance of witness protection programs, the problem of governmental reprisals against individuals or groups who have cooperated with a UN human rights inquiry, the need to regulate the use of lethal force by law enforcement officers, shoot-to-kill policies, the relationship between human rights law and international humanitarian law, mercy killings in times of armed conflict, and the need to make military justice systems human rights compatible. With respect to the death penalty, Alston's reports discussed the need for transparency, the unacceptability of the mandatory death penalty under international law, the definition of the 'most serious crimes' for which the death penalty may be imposed, the right to seek pardon or commutation of a death sentence, and the juvenile death penalty.
In 2014, Alston was appointed UN Special Rapporteur on extreme poverty and human rights.
In late October 2016, Alston released a scathing report to the UN General Assembly, calling the UN's refusal to accept responsibility for the devastating cholera outbreak a "disgrace." The report criticized the "flawed and unfounded" advice given by the UN's Office of Legal Affairs (OLA), that he blames for preventing the UN from accepting responsibility for the outbreak. According to Alston, “The UN’s explicit and unqualified denial of anything other than a moral responsibility is a disgrace. If the United Nations bluntly refuses to hold itself accountable for human rights violations, it makes a mockery of its efforts to hold governments and others to account.” Alston also critiques the United States, the main contributor to the UN Peacekeeping budget, and its unwillingness to publicly state its legal position on the responsibility of the UN for causing cholera in Haiti. In his opening and closing statements, Alston called on advocacy groups like the Boston-based Institute for Justice and Democracy in Haiti (IJDH) and the Haiti-based Bureau des Avocats Internationaux (BAI) to continue their work, and to keep up pressure on UN Member States.
Alston also directed a project funded by the European Commission, which resulted in the publication of a Human Rights Agenda for the European Union for the Year 2000 and a 1999 volume of essays (The European Union and Human Rights). Many of its recommendations were subsequently implemented by the European Commission and the European Council. He also is one of 29 signatories to the Yogyakarta Principles.
Alston has written on issues such as economic, social and cultural rights, United Nations institutions and procedures, labour rights, the role of non-state actors in relation to human rights, comparative bills of rights, the use of force, and human rights and development policies. He is also one of the authors of a textbook in the field entitled International Human Rights in Context, Law, Politics, Morals, published by Oxford University Press. A third edition was published in 2007.