McMahon has been chief financial officer since 2014 for Hologic, Inc., an innovative medical technology company, primarily focused on improving women's health and well-being, based in Massachusetts, USA. In 2017, Hologic had revenues of $3.1 billion, spanning breast and skeletal health, diagnostics, surgical and aesthetic products. Prior to Hologic, McMahon spent 20 years with Johnson & Johnson, most recently as worldwide vice president of finance and business development for Ortho Clinical Diagnostics, a division of Johnson & Johnson’s Medical Device and Diagnostics Group. Prior to that he held a variety of financial leadership positions within Johnson & Johnson after joining the company in 1993. McMahon began his career with Harris Corporation in Florida.