- 1939 born in Colombo, Sri Lanka; Swiss citizen
- 1958 – 1965 law studies in Zurich and Stockholm
- 1965 awarded degree of Dr. iur. from the University of Zurich with a dissertation on the Swedish Ombudsman
- Clerkship at a District Court
- 1967 admission to the Bar, Canton of Zurich
- 1967/68 law clerk at the Superior Court (Obergericht) of the Canton of Zurich
- 1969 visiting research scholar at the University of Michigan Law School; based on this research, publication of a book on the U.S. Supreme Court and Politics (1972)
- 1970 – 1972 research assistant, University of Zurich; recognition as a university lecturer (Habilitation) in constitutional and administrative law
- Autumn 1972 – autumn 1975 Secretary General of the Council of the Federal Institutes of Technology
- Autumn 1975 – summer 2004 professor of constitutional law, administrative law and comparative constitutional law, University of Zurich; from 1990 until 2004 Director of the Institute of Public International Law and Comparative Constitutional Law. Dean of the Law Faculty 1990 – 1992.
- Research during sabbaticals at the University of Michigan Law School and at the universities of Aix/Marseille, Pisa and East Anglia.
- Co-author of books on Swiss and comparative constitution law which are widely used in teaching at universities as well as in legal practice.
- In his numerous publications Haller has emphasised the need to compare constitutional orders and to analyse constitutional issues (such as fundamental rights, systems of government and constitutional adjudication) in a comparative context. Many articles focus on the ombudsman institution.
- 2004 – 2010: following retirement teaching engagements in constitutional law and comparative constitutional law at the universities of Lucerne (2005), St. Gallen (2004 – 2008), Zurich (2009 and 2010) and at the Duke Geneva Institute in Transnational Law (summer course 2011). Further publications, among others a book on “The Swiss Constitution in a Comparative Context” (2009).
- 1976 – 1989 Associate Judge of the Administrative Court of the Canton of Zurich
- 1979 – 1987 member of the board of Zurich’s Law Association; chairman 1983 – 1985
- 1995 – 2002 member of the Foundation Council of the Swiss National Science Foundation
- Member of the Research Committee of the International Ombudsman Institute (until 1988), special award of the International Ombudsman Institute (conferment at the Fourth International Ombudsman Conference in Canberra, 1988)
- Since 2004 honorary member of the Association of Swiss Parliamentary Ombudsmen