He is one of the leading contemporary epistemologists, and has also written on metaphysics, modern philosophy and philosophy of mind. In his books Knowledge in Perspective (1991) and A Virtue Epistemology (2007), Sosa defends a form of virtue epistemology called "virtue perspectivism", which distinguishes animal knowledge from reflective knowledge. Sosa earned his BA and MA from the University of Miami and his PhD from the University of Pittsburgh where his dissertation was supervised by Nicholas Rescher. He then went to Brown University, where he came under the philosophical influence of fellow professor Roderick Chisholm. His son, David Sosa, is associate professor of Philosophy at the University of Texas, Austin.

Sosa is a past president of the American Philosophical Association and a Fellow of the American Academy of Arts & Sciences.

He edits the philosophical journals Noûs and Philosophy and Phenomenological Research. In 2005, he delivered the John Locke Lectures at Oxford., which formed the basis of his 2007 book.