He attended Bristol Grammar School (1949–1956) and then was an Open Scholar in Classics at Corpus Christi College, Oxford.
From 1961 he pursued graduate studies as a State Student at Oxford, spending the year 1961–1962 in Rome (where he worked with J.B. Ward-Perkins), and was then the T.W.
[citation needed] From 1964 to 1965 Harris served as Lecturer in Ancient History at Queen's University, Belfast.
One reviewer wrote: "In the process of evolving his interpretation, he treads on the toes of a majority of the living scholars (and a large number of deceased ones) who have interested themselves in this problem.
In the same period Harris began to work extensively on economic history, publishing a series of papers about slavery, money and other issues that were collected in Rome's Imperial Economy (2011).
In the 1990s he began to work intensively on psychological aspects of ancient history, and in 2001 he published Restraining Rage: the Ideology of Anger Control in Classical Antiquity.
In October 2017, a Columbia University doctoral student, identified as Jane Doe, filed suit in the U.S. District Court for Southern New York against Harris and the trustees of Columbia University, alleging that Harris had repeatedly sexually harassed her throughout the years 2014 and 2015.