Dr McIlwraith obtained his veterinary degree from Massey University, New Zealand, was in practice in New Zealand and the UK followed by an internship at the University of Guelph, Canada and a surgical residency at Purdue University. He also obtained MS and PhD degrees from Purdue University. He is A Diplomate of the American College of Veterinary Surgeons, the European College of Veterinary Surgeons, the American College of Veterinary Sports Medicine and Rehabilitation, and a Fellow of the Royal College of Veterinary Surgeons

Since 1979 he has been a faculty member at Colorado State University. Currently he is a University Distinguished Professor, holds the Barbara Cox Anthony University Endowed Chair in Orthopaedics and is the Founding Director of the Orthopaedic Research Center. He also has a referral equine orthopaedic surgical practice based in Southern California and is a consultant and surgeon for clients elsewhere in the US and Ireland, England, France and New Zealand.
His research interests focus on equine orthopaedic surgery and translational joint disease research including novel treatments for osteoarthritis and articular cartilage repair, mesenchymal stem cell therapies and early diagnosis of osteoarthritis and pre-fracture disease using imaging and fluid biomarkers. He has authored six textbooks, over 450 scientific publications and textbook chapters and has presented over 700 seminars and workshops, both nationally and internationally to equine practitioners, veterinary specialty groups and human orthopaedic meetings.

Honors include doctoral degrees (honoris causa) from the University of Vienna (1995), Purdue University (2001), Massey University (2003), the University of Turin (2004) and the University of London (2010). Awards received include the Schering-Plough Award for equine research for his contributions to orthopaedic research by the World Eaquine Veterinary Association (1995), the  Frank Milne Lecture (Lifetime Contribution Award) from American Association of Equine Practitioners (2005), induction into the international Equine Research Hall of Fame (2005), the Founders Award for Lifetime Achievement from American College of Veterinary Surgery (2006), the John Hickman Award for Equine Orthopaedics from the British Equine Veterinary Association (BEVA) (2006), the Markowitz Award from the Academy of Surgical Research (2013), the Marshall R. Urist MD Award for Excellence in Tissue Regeneration Research from the Orthopaedic Research Society (2014), Honorary Fellow of the International Cartilage Research Society (2018), Schofield Memorial Lecture and Medal, Ontario Veterinary College, University of Guelph (2018), the American Association of Equine Practitioners Research Award (2018), the American Veterinary Medical Association (AVMA) Lifetime Excellence in Research Award (2019), the ACVS Foundation Legends Award (2019) and the New Zealand Equine Veterinary Association Brian Goulden Prize for Outstanding NZ Equine Veterinarian (2020).He was also honored with the opening of the C. Wayne McIlwraith Translation Medicine Institute at Colorado State University in May 2019