[2] McMahon graduated in mechanical engineering from the University of Bristol in 1978; prior to working in the railway and then automotive industries.
[2] His research on computer aided design and manufacture (CADCAM) includes the introduction of a general purpose ontology-driven annotation approach for recording view-point dependent information in CAD,[3] and work on the use of parametric and associative CAD systems to support the complex and lengthy design activities in the automotive industry.
[5] In a 2006 paper, hen proposed an information accessing framework using computational classification technologies.
Together with Jimmie Browne of the National University of Ireland, Galway, in 1992 McMahon published a textbook on computer-aided design and manufacture CADCAM From Principles to Practice (second edition, 1998).
[12] In 2020, McMahon published a translation of Philippe Bihouix's book, The Age of Low Tech: Towards a Technologically Sustainable Civilization.