Kastrup is the executive director of Essentia Foundation, which curates and publishes "the latest analytic and scientific indications that metaphysical materialism is fundamentally flawed".

His doctoral dissertation was Analytic Idealism: A consciousness-only ontology,[3] which articulated the metaphysical position he would continue to develop and for which he would become most widely known.

[citation needed] Kastrup began his career in academia and technological research by contributing to areas such as artificial intelligence and information security.

[4][5] He has written for numerous publications, including Scientific American,[6] where his articles critique physicalist interpretations of consciousness and offer an idealist alternative.

[8][9][10] Kastrup has engaged in a number of public debates with prominent figures in both science and philosophy, including neuroscientist Christof Koch, philosopher Graham Oppy, lecturer/writer Susan Blackmore, cognitive scientist Donald D. Hoffman, philosopher Philip Goff, and physicist and science educator Sabine Hossenfelder.