Robert Thomas Seeley (born February 26, 1932, in Bryn Mawr, Pennsylvania, USA) is a mathematician who works on pseudo differential operators and the heat equation approach to the Atiyah–Singer index theorem.
Seeley did his undergraduate studies at Haverford College, and earned his Ph.D. from the Massachusetts Institute of Technology in 1959, under the supervision of Alberto Pedro Calderón. He taught at Harvey Mudd College and then in 1962 joined the faculty of Brandeis University. In 1972 he moved to the University of Massachusetts Boston, where he is now an emeritus professor. In 2012 he became a fellow of the American Mathematical Society.