Mathieu is an Associate Professor of Diagnostic Imaging at the School of Veterinary Medicine at the University of California, Davis, where he has been a faculty member since 2007. He earned his DVM degree from the National Veterinary School of Lyon in France in 2002 and a Master's degree from the University of Montreal in Canada in 2004.

After completing his radiology residency at the University of Pennsylvania, Mathieu became a diplomate of both the American College of Veterinary Radiology and the European College of Veterinary Diagnostic Imaging in 2007.

Mathieu's research focuses on musculoskeletal imaging in horses, with over 50 publications in peer-reviewed journals. He has been a pioneer in the use of positron emission tomography (PET) in horses, contributing to the development of both research and clinical applications.