Harnad was born in Budapest, Hungary. He did his undergraduate work at McGill University and his graduate work at Princeton University's Department of Psychology. Harnad completed his Master of Arts degree in Psychology from McGill University in 1969, his Doctor of Philosophy degree from Princeton University in 1992. He was awarded an honorary doctorate by University of Liège in 2013.
Harnad's research interests are in cognitive science and open access. He is currently Canada Research Chair in cognitive science at Université du Québec à Montréal (UQAM) and professor of cognitive science at the University of Southampton. He was elected external member of the Hungarian Academy of Sciences in 2001. His research is on categorization,communication, cognition, and consciousness and he has written extensively on categorical perception, symbol grounding, origin of language, lateralization, the Turing test, distributed cognition, scientometrics, and consciousness. Harnad is a former student of Donald O. Hebb and Julian Jaynes.
In 1978, Harnad was the founder of Behavioral and Brain Sciences, of which he remained editor-in-chief until 2002. In addition, he founded Psycoloquy (an early electronic journal sponsored by the American Psychological Association), CogPrints (an electronic eprint archive in the cognitive sciences hosted by the University of Southampton), and the American Scientist Open Access Forum (since 1998; now the Global Open Access List, GOAL). Harnad is an active promoter of open access (EPrints, EnablingOpenScholarship (EOS), Open Access Scholarly Information Sourcebook (OASIS), SPARC Campus Open Access Policies).
Harnad is the author of a 2011 open letter signed by over 60 external members of the Hungarian Academy of Sciences addressed to the Academy's President, József Pálinkás, concerning the press and police harassment campaign against Hungarian philosophers who were critics of the current Hungarian ruling party, Fidesz, and its prime minister, Viktor Orbán.
Harnad is also on the Board of Directors of the Canadian-Hungarian Democratic Charter ] an organization launched in 2011 on the 55th anniversary of the Hungarian Revolution of 1956 against Russian domination. According to its definition, the charter's goal is to help support democracy in Hungary against what it sees as the increasingly undemocratic developments currently taking place under Viktor Orban and the Fidesz party.
Harnad is a vegan, and is increasingly active in animal welfare and animal rights.