Paul Townsend made important contributions to the original formulation of supergravity, which is a generalisation of general relativity that unifies bosons and fermions. He subsequently originated many of the most significant ideas in the theory of the solitons of supergravity theories, known as supermembranes, and elucidated the significance of these objects in the underlying structure of string theory. Of particular importance was his development in 1994 of non-perturbative duality symmetries in string theory that led to a unified understanding of all superstring theories together with supergravity. This has transformed the study of string theory and led to its generalisation, known as ‘M theory’.