Professor Leigh has been investigating streptococci of significance to diseases of human and  livestock populations since 1987. This work, originally conducted at IAH-Compton was relocated to University of Oxford in 2005 before finally arriving at the School of Veterinary Medicine & Science at the University of Nottingham in 2007. Professor Leigh's research interests range from investigation of host pathogen interactions involved in bacterial pathogenesis and studies on protein structure in relation to function and teh use of moelcular tools to enable this.  Professor Leigh's research has been strategically focused at the control of disease and has attracted considerable commercial collaboration.

Professor Leigh's current research activity is focused on functional genomics of bacteria in relation to infectious disease. This is particularly aimed at diseases caused by Streptococci. With strategic aims of identification of coding and non-coding sequences that play key roles during disease pathogenesis and the consequence of sequence variation in the bacterial population. To aid with the initial stages (gene identification) his research group have developed a simple and rapid genome wide mutation mapping system (PIMMS) that produces similar outputs to Tradis and Tnseq. The output is of value to the pharmaceutical industry in the identification of sub-units for vaccines, targets for new therapies, gene targets for rational attenuation. For academia, it identifies networks of genes (products) for further definition of their role and mechanistic analysis in vitro.