Marcelo Gleiser (born 1959 in Rio de Janeiro) is a Brazilian physicist and astronomer. He received his bachelor's degree in 1981 from the Pontifícia Universidade Católica do Rio de Janeiro, his M.Sc. degree in 1982 from the Universidade Federal do Rio de Janeiro, and his Ph.D. in 1986 from King's College London. After this he worked as a postdoc at Fermilab until 1988 and from then until 1991 at the Kavli Institute for Theoretical Physics. Since 1991, he has taught at Dartmouth College, where he was awarded the Appleton Professorship of Natural Philosophy in 1999, and is currently a professor of physics and astronomy.

Gleiser's current research interests include the physics of the early Universe, the properties of solitons in quantum field theories, and questions related to the origin of life on Earth and elsewhere in the Universe. The author of over eighty papers in peer-reviewed journals, Gleiser has also written two popular books on cosmology and religion, The Prophet and the Astronomer and The Dancing Universe. Apart from many contributions to magazines and newspapers in the US and abroad, Gleiser writes a weekly science column in a supplement of the Brazilian Folha de São Paulo newspaper. He is a Fellow of the American Physical Society and has been awarded the Presidential Faculty Fellows Award from the White House and the National Science Foundation. In Brazil, he received the José Reis Award for the Public Understanding of Science from the Brazilian National Research Council. He has been featured in several TV documentaries, including "Stephen Hawking's Universe, and the History Channel's "Beyond the Big Bang" (2007) and "How Life Began" (2008). In Brazil, his two science series for TV Globo's "Fantastico" were watched by over 30 million viewers.