Hardy's first major publication was a collection of writings by Arnold Mallinson, an eccentric Oxford clergyman with whom he lodged for a time; he published this work under his own imprint (Robert Dugdale). He also, while still a student, composed a number of musical pieces, which were published many years later as Tunes: Collected Musical Juvenilia (2003).
In addition to publishing under the pseudonym Robert Dugdale (since 1974), Hardy worked as an editor at Oxford University Press for many years (1977–1990); he has been a Fellow of Wolfson College since 1990.
Hardy's most significant contribution to scholarship has been his editing of the writings of Isaiah Berlin.
When Hardy met Berlin in 1972, Berlin was at the height of his fame as an intellectual figure; but he was viewed as not having written very much, and many doubted if he would leave a lasting contribution to scholarship beyond a small number of scattered essays. Hardy's research revealed that Berlin had published well over 150 pieces by the late 1970s.
His subsequent editing of Berlin's essays made Berlin's most important work widely available. In 1990 Hardy abandoned his career in publishing to work full-time on Berlin's unpublished essays, lectures, and correspondence. He has thus far produced 15 volumes of Berlin's writings, as well as the first volume of a 4-volume edition of Berlin's letters.
Henry Hardy married Anne Wilkinson in 1979. They have two children, Ellen (b. 1983) and Michael (b. 1985).