Howarth taught at Princeton from 1966, offering over 60 undergraduate and graduate courses, from "Moby-Dick Unbound" to "Race and Place" and "Darwin in our Time."
[3] Howarth began his career as a specialist in American literary manuscripts and textual criticism, and in 1972 he became editor in chief of The Writings of Henry D. Thoreau.
Howarth later expanded his studies in literary nonfiction to include the fields of autobiography, journalism, trans-Atlantic romanticism, and the literature of place and travel.
[5] Howarth was a founding member of the Princeton Environmental Institute and among the earliest scholars to define and explore the field of literary ecocriticism.
His essay "Some Principles of Ecocriticism" describes the origins and evolution of this field from early work in ecology, ethics, language, criticism, geography, natural and social sciences, history, literature, American studies, and media.