He has since written numerous articles on eighteenth-, nineteenth-, and twentieth century art. With David Prochaska he published Beyond East and West: Seven Transnational Artists in 2004. With Vernon Burton he edited the volume Remembering Brown at Fifty: The University of Illinois Commemorates Brown v. Board of Education, a collection of essays addressing the landmark Supreme Court decision.
A volume edited by O’Brien on the theme of civilization in nineteenth-century art is set to appear next year from Manchester University Press, and he has just completed a book manuscript on the theme of civilization in the art of Eugène Delacroix.
He has received major grants from the Terra Foundation, the American Council of Learned Societies, and the Institute of Advanced Study in Princeton.