Harman was born in Iowa City and raised in Mount Vernon, Iowa. He received a B.A. from St. John's College in Annapolis, Maryland in 1990 and went on to graduate school at Penn State University to earn a master's degree, studying under philosopher Alphonso Lingis, in 1991. While pursuing a Ph.D. at DePaul University, Harman worked as an online sports reporter, an experience which he credits for developing his writing style and productivity. After finishing his degree in 1999 he joined the Department of Philosophy at the American University in Cairo, where he has taught since 2000.
Harman starts the development of his work with Martin Heidegger's concept of "tool-analysis" from Being and Time. To Harman, tool-analysis was a key discovery which establishes the groundwork for taking seriously the autonomous existence of objects and, in doing so, highlights deficiencies in phenomenology due to its subordination of objects to their use by or relationship with humans.
Harman is considered part of the speculative realism trend, a nebulous grouping of philosophers united by two perspectives: a rejection of anthropocentric "philosophies of access" which privilege the perspective of humans in relation to objects, and a support of metaphysical realism via rejection of "correlationism", an assumption in Post-Kantian philosophy that fellow speculative realist Quentin Meillassoux defines as "the idea according to which we only ever have access to the correlation between thinking and being, and never to either term considered apart from the other." Harman's object-oriented approach considers the life of objects to be fertile ground for a metaphysics that works to overcome anthropocentrism and correlationism.
According to Harman, everything is an object, whether it be a mailbox, a shadow, spacetime, a fictional character, or the Commonwealth of Nations. However, drawing on phenomenology, he does distinguish between two categories of objects: real objects and sensual objects (or intentional objects), which sets his philosophy apart from the flat ontology of Bruno Latour.
Harman defines real objects as inaccessible and infinitely withdrawn from all relations and then puzzles over how such objects can be accessed or enter into relations: "by definition, there is no direct access to real objects. Real objects are incommensurable with our knowledge, untranslatable into any relational access of any sort, cognitive or otherwise. Objects can only be known indirectly. And this is not just the fate of humans — it’s the fate of everything. Fire burns cotton stupidly ..."
Central to Harman's philosophy is the idea that real objects are inexhaustible: "A police officer eating a banana reduces this fruit to a present-at-hand profile of its elusive depth, as do a monkey eating the same banana, a parasite infecting it, or a gust of wind blowing it from a tree. Banana-being is a genuine reality in the world, a reality never exhausted by any relation to it by humans or other entities." (Harman 2005: 74). Because of this inexhaustibility, claims Harman, there is a metaphysical problem regarding how two objects can ever interact. His solution to this problem is to introduce the notion of "vicarious causation", according to which objects can only ever interact on the inside of an "intention" (which is also an object).
Cutting across the phenomenological tradition, and especially its linguistic turn, Harman deploys a brand of metaphysical realism that attempts to extricate objects from their human captivity and metaphorically allude to a strange subterranean world of "vacuum-sealed" objects-in-themselves: "The comet itself, the monkey itself, Coca-Cola itself, resonate in cellars of being where no relation reaches."
Expressing strong sympathy for panpsychism, Harman proposes a new philosophical discipline called "speculative psychology" dedicated to investigating the "cosmic layers of psyche" and "ferreting out the specific psychic reality of earthworms, dust, armies, chalk, and stone." Harman does not, however, unreservedly endorse an all-encompassing panpsychism and instead proposes a sort of polypsychism that nonetheless must "balloon beyond all previous limits, but without quite extending to all entities". He continues by stating that "perceiving" and "non-perceiving" are not different kinds of objects, but can be found in the same entity at different times: "The important point is that objects do not perceive insofar as they exist, as panpsychism proclaims. Instead they perceive insofar as they relate."
Harman rejects scientism on account of its anthropocentrism: "For them, raindrops know nothing and lizards know very little, and some humans are more knowledgeable than others."