Mark Stephen Wrighton (born 1949) is an American academic, a chemist, and the current Chancellor of Washington University in St. Louis. Born in Jacksonville, Florida, Wrighton received his B.S. in Chemistry from Florida State University in 1969. While at Florida State, he won the Monsanto Chemistry Award for outstanding research. He received his Ph.D at the age of 22 from the California Institute of Technology, working under Harry B. Gray and George S. Hammond. His doctoral dissertation subject was Photoprocesses in Metal-Containing Molecules. He graduated from Caltech in 1972.

Wrighton joined the faculty of the chemistry department at the Massachusetts Institute of Technology in the fall of 1972 as an assistant professor. In 1976, he was promoted to associate professor and was made a full professor the following year. Wrighton held the Frederick G. Keyes Chair in Chemistry from 1981 to 1989, when he was given the newly endowed Ciba-Geigy Chair in Chemistry.

In 1987, Wrighton became the head of MIT's chemistry department. He became MIT's provost in 1990. In 1995, Wrighton had the honor of giving the commencement address at Caltech. That same year, he left MIT to become chancellor of Washington University in St. Louis.

Wrighton's research interests are centered around photochemistry and metal catalysts. He has written more than 300 journal articles and holds 14 patents. During his time at MIT, Wrighton supervised the doctoral research of more than 70 students.

In early 2007 Wrighton had been mentioned as a candidate for Harvard University's presidency. Committee members noted Wrighton's past experience as a chemist as a factor in including him on their list. The committee chose Drew Gilpin Faust to replace Derek Bok instead.