Professor O'Sullivan grew up in a small town in New Hampshire, where he attended the local public high school. He received his B.A. in philosophy from Davidson College in 1992. After a year hiatus, he moved to Berkeley, CA to enter the Ph.D. program in philosophy at the University of California. He completed the requirements for his doctorate in the spring of 2002.

He joins the Rhodes philosophy department after having taught at Davidson since the spring of 2000. His primary research interest lies in the philosophy of mind. Working with John Searle, he wrote his dissertation on the tension between treating mentality as both irreducible and as causally efficacious.

His most recent work has focused on evaluating Saul Kripke’s argument against the mind-brain identity theory.