Graeme Bryce Segal  (born 21 December 1941) is an Australian mathematician, and professor at the University of Oxford.Segal was educated at the University of Sydney, where he received his BSc degree in 1961. He went on to receive his D.Phil. in 1967 from St Catherine's College, Oxford; his thesis, written under the supervision of Michael Atiyah, was titled Equivariant K-theory.

His thesis was in the area of equivariant K-theory. The Atiyah–Segal completion theorem in that subject was a major motivation for the Segal conjecture, which he formulated. He has made many other contributions to homotopy theory in the past four decades, including an approach to infinite loop spaces. He was also a pioneer of elliptic cohomology, which is related to his interest in topological quantum field theory.He was awarded the Sylvester Medal by the Royal Society in 2010for his highly influential and elegant work on the development of topology, geometry and quantum field theory, bridging the gap between physics and pure mathematics.