Thomas Arthur Steitz (born August 23, 1940) is a Sterling Professor of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University, New Haven, Connecticut, USA. Steitz was awarded the 2009 Nobel Prize in Chemistry along with Venkatraman Ramakrishnan and Ada Yonath "for studies of the structure and function of the ribosome".

He received a Ph.D. in biochemistry and molecular biology from Harvard University in 1966 where he worked under direction of subsequent 1976 chemistry Nobel Prize winner William N. Lipscomb, Jr.
He did his postdoctoral research as a Jane Coffin Childs Postdoctoral Fellow at the MRC Laboratory of Molecular Biology at Cambridge University during 1967-1970. He was also a Macy Fellow doing research at the University of Göttingen during 1976-1977 and a Fairchild Scholar at Caltech during 1984-1985.
Steitz also won the Gairdner International Award in 2007 "for his studies on the structure and function of the ribosome which showed that the peptidyl transferase was an RNA catalyzed reaction, and for revealing the mechanism of inhibition of this function by antibiotics".