Simon has made a significant contribution to the study of evolutionary ecology of birds over his research career. His research niche has been understanding the determinants of evolutionary fitness amongst individuals within populations, in the context of mating, parental and social behaviour. Using a variety of species, Simon has examined these research questions using systems in which genetic structuring provides an opportunity for greater insight, such as the polymorphic Gouldian finch and the hybridising subspecies of long-tailed finch. An important focus of work has been the well-worked zebra finch, with Simon establishing and running the longest population study of wild birds that helps to contextualise the captive research focused on this species around the world.

A major focus of current work is the intersect between physiology and environmental variation and its contribution to fitness in the context of organismal responses to major challenges such as extreme heatwaves, and heavily contaminated environments (e.g. heavy metal contamination in mining towns). 

Simon has published over 200 peer-reviewed papers in his career to date, since completing his PhD (University of Leicester, UK, 1998). He spent his early career in Europe (Uppsala University, Sweden; Oxford University, UK; Imperial College London, UK), before moving to Australia in 2004 (University of New South Wales). He has been based at Macquarie University since 2007 where he has held two prestigious research fellowships (ARC QEII Fellowship 2008-2012 & ARC Future Fellowship 2014-2017) and an ongoing academic position. 

Simon has always maintained a broad range of international collaborations with active projects with multiple colleagues in the US, UK, and the Netherlands, providing a good training platform for his postgraduate students. Since 2007, 17 PhD students have completed their PhD’s under his primary supervision.