Tom Michael Fenchel (born 19 March 1940, in Copenhagen) is a Danish marine ecologist and professor first at the University of Aarhus, later at the University of Copenhagen. He is a highly cited scientist^[1] and known for, among other things, Fenchel's Law.

Fenchel holds PhD (1964) and Doctor of Science (1969) degrees, both from the University of Copenhagen.

He is a foreign member of the Royal Society^[2] and a reviewing editor of the scientific journal Science.^[3] He was the 1986 recipient of the ECI Prize of ecology and wrote the book ^[4] in the ECI Prize laureate series Excellence in Ecology. He served as president 2004-2008 of the Royal Danish Academy of Sciences and Letters (he has been a member since 1976). In 2006 he was awarded the A.C. Redfield Lifetime Achievement Award by the American Society of Limnology and Oceanography.

He is a member of the Norwegian Academy of Science and Letters^[5] and of the American National Academy of Sciences^[6]