Stephen Louis Macknik is an American neuroscientist and science writer. He is a Professor of Ophthalmology, Neurology, and Physiology & Pharmacology at the State University of New York, Downstate Medical Center, where he directs the Laboratory of Translational Neuroscience. He directed laboratories previously at the Barrow Neurological Institute and University College London. He is best known for his studies on illusions, consciousness, attentional misdirection in stage magic, and cerebral blood flow.

Macknik is a founding member of the Neural Correlate Society. He serves on the Advisory Board of Scientific American: Mind, and on the Leadership Team of the Center for Emergency Management and Homeland Security at Arizona State University.

In 2001, Macknik moved to the United Kingdom, as a Lecturer in Ophthalmology and laboratory director at University College London. In 2004, he returned to the United States as an Assistant Professor, and later, Associate Professor, at the Barrow Neurological Institute in Phoenix, Arizona, where he directed the Laboratory of Behavioral Neurophysiology. In 2014, he moved to Brooklyn, NY, as Professor of Ophthalmology, Neurology, and Physiology & Pharmacology at SUNY Downstate Medical Center, where he directs the Laboratory of Translational Neuroscience. He serves on the editorial board of the scientific journal PeerJ.