After some time working in mixed practices in Hertfordshire and Malton, North Yorkshire, David joined Greenwood Ellis & Partners in 1989 and became a partner in 1995. He has responsibility for a number of Thoroughbred stud farms and racing stables and has a particular interest in the control of inflammatory airway disease in horses in training.
David obtained his Certificates in Equine Practice in 1990 and in Equine Stud Medicine in 1992. He held the position of Chief Examiner for the Royal College of Veterinary Surgeons in Equine Stud Medicine for several years and has lectured regularly at the TBA Stud Farming Course, the National Stud and Cambridge University. David joined the Council of the British Equine Veterinary Association (BEVA) in 1998 and in 2008 became President. From 2012-2018 he acted as Veterinary Advisor to the Racecourse Owners Association and is Veterinary Advisor to the sales company Tattersalls. He is Chairman of the Trustees of the University of Cambridge Veterinary School Trust. Since 2010 he has acted as Managing Partner.