Fotini G. Markopoulou-Kalamara is a Greek theoretical physicist interested in foundational mathematics and quantum mechanics. She is a faculty member at Perimeter Institute for Theoretical Physics and is an adjunct professor at the University of Waterloo.

Markopoulou received her PhD from Imperial College London and held postdoctoral positions at the Albert Einstein Institute, Imperial College, and Penn State University. She shared First Prize in the Young Researchers competition at the Ultimate Reality Symposium in Princeton, New Jersey. She has been influenced by researchers such as Christopher Isham who call attention to the unstated assumption in most modern physics that physical properties are most naturally calibrated by a real-number continuum. She, and others, attempt to make explicit some of the implicit mathematical assumptions underpinning modern theoretical physics and cosmology.

In her interdisciplinary paper "The Internal Description of a Causal Set: What the Universe Looks Like from the Inside", Markopoulou instantiates some abstract terms from mathematical category theory to develop straightforward models of space-time. It proposes simple quantum models of space-time based on category-theoretic notions of a topos and its subobject classifier (which has a Heyting algebra structure, but not necessarily a Boolean algebra structure).

In May 2006, Markopoulou published a paper with Lee Smolin that further popularized this Causal Dynamical Triangulation (CDT) Theory by explaining time slicing of the Ambjorn–Loll CDT model as result of gauge fixing. Their approach relaxed the definition of the Ambjorn–Loll CDT model in 1 + 1 dimensions to allow for a varying lapse. In 2008, Markopoulou, Tomasz Konopka and Simone Severini initiated the study of a new background independent model of evolutionary space called quantum gravity.