Professor Kirby worked as a GP in Letchworth, Hertfordshire. He also worked in the cardiology department at the Queen Elizabeth II Hospital, for 36 years, and provided an open-access echocardiography service for patients with heart failure for the local Primary Care Trust. He was Visiting Professor to the Faculty of Health and Human Sciences, at the University of Hertfordshire. His subsequent clinical work was at The Prostate Centre in London, where he dealt with complex cardio-metabolic diseases, sexual problems and andrology. He has been a long-term member of the British Society for Sexual Medicine. An Associate Member of the British Association of Urological Surgeons, a Fellow of the Royal College of Physicians, and Current editor of Trends in Urology & Men’s Health. He also holds membership of several NHS advisory boards, and is a member of the scientific advisory group to The Prostate Cancer Risk Management Programme. He has published more than 450 clinical papers and 33 books. The 4th edition of Men’s Health, and, also, Testosterone in Cardiometabolic and other diseases were published in 2022.