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

After graduating, in 1946, he worked at the Polytechnic Institute of Brooklyn. In 1952, at the University of North Carolina, he developed Rice-Ramsperger-Kassel-Marcus theory by combining RRK theory with transition state theory. In 1964, he taught at the University of Illinois.

A type of chemical reaction linked to his many studies of electron transfer would be the transfer of an electron between metal ions in different states of oxidation. An Example of this type of chemical reaction would be one between a bivalent and a trivalent iron ion in an aqueous solution. In Marcus's time chemists were astonished at the slow rate in which this specific reaction took place. This attracted many chemists in the 1950s and is also what began Marcus's interests in electron transfer. Marcus made many studies based on the principles that were found within this chemical reaction, and through his studies was able to create his famous Marcus theory. This theory gave way to new experimental programs that contributed to all branches within chemistry.

He was elected to the National Academy of Sciences in 1970, the American Academy of Arts and Sciences in 1973, the American Philosophical Society in 1990, received honorary membership in the Royal Society of Chemistry in 1991, and in the Royal Society of Canada in 1993. He was elected a Foreign Member of the Royal Society (ForMemRS) in 1987.

He also received a Professorial Fellowship at University College, Oxford from 1975 to 1976.

Honorary degrees were conferred to Marcus by the University of Chicago in 1983, by the University of Goteborg in 1986, by the Polytechnic Institute of Brooklyn in 1987, by McGill in 1988, by Queen's University in 1993, by the University of New Brunswick also in 1993 and by the University of Hyderabad, in India, which conferred the degree of Doctor of Science in 2012.

Before receiving the Nobel Prize in 1992, Marcus received the National Medal of Science in 1989, the Irving Langmuir Award of the American Chemical Society in 1978, the Willard Gibbs Award in 1988, the Theodore william Richards Award in 1990, the Pauling Medals in 1991, and the Remsen and Edgar Fahs Smith Awards in 1991, the Peter Debye Award of the American Chemical Society in 1988, the Robinson Award in 1982, the Centenary Medals of the Faraday Division of the Royal Society of Chemistry in 1988, Columbia University's Chandler Medal in 1983, Ohio State's william Lloyd Evans Award in 1990, the Wolf Prize in Chemistry in 1985 and the Hirschfelder Prize in Chemistry in 1993. Marcus has been a Member of the National Academy of Sciences since 1970, and a Member of the American Academy of Arts and Sciences since 1973. He won the Wolf Prize in Chemistry in 1984.

Electron transfer is one of the simplest forms of a chemical reaction. It consists of one outer-sphere electron transfer between substances of the same atomic structure likewise to Marcus’s studies between bivalent and trivalent iron ions. Electron transfer may be one of the most basic forms of chemical reaction but without it life cannot exist. Electron transfer is used in all respiratory functions as well as photosynthesis. In the process of oxidizing food molecules, 2 hydrogen ions, 2 electrons, and an oxygen molecule react to make an exothermic reaction as well as H₂O (water). Due to fact that electron transfer is such a broad, Common, as well as essential reaction within nature, Marcus's theory has become vital within the field of chemistry.