Rudolph "Rudy" Arthur Marcus (born July 21, 1923) is a Canadian-born chemist who received the 1992 Nobel Prize in Chemistry for his theory of electron transfer. Marcus theory, named after him, provides a thermodynamic and kinetic framework for describing one electron outer-sphere electron transfer.

He earned a B.Sc. in 1943 and a Ph.D. in 1946, both from McGill University.
In 1958, he became a naturalized citizen of the United States.