Leigh developed CIRCLY, the Windows-based package that can analyse a range of load types acting on layered elastic systems. CIRCLY was first released in 1977 and was commercialised by MINCAD Systems in 1988. The first Windows version appeared in 1996. CIRCLY is an integral part of the Austroads Pavement Design Guide used by authorities throughout Australia and New Zealand. Leigh joined CSIRO Division of Geomechanics in 1970 after qualifying in Applied Mathematics & Physics from Monash University. Over the 18 years of his career with CSIRO he worked on numerical stress analysis techniques.
In 1988, Leigh formed Mincad Systems, a company specialising in numerical stress analysis for the civil and mining industries and since 1993 has specialised in pavement applications. In 2018, version 7.0 of Circly was released.
In 1995, a special version of CIRCLY was released for airport pavement design (APSDS- Airport Pavement Structural Design System) in conjunction with Pioneer Road Services and the Federal Airports Corporation. In 2005 Leigh released HIPAVE (Heavy Industrial Pavement) for Heavy Industrial Pavements such as intermodal container terminal pavements. Leigh is also co-author of the recently released Heavy Duty Industrial Pavement Design Guide – a guide that reflects best practice in the design of new construction and rehabilitation of industrial pavements.