Warren graduated in 1991 and took up a position as a vocational trainee at a busy NHS dental practice in the West Midlands. Shortly after completing his vocational training, he purchased the practice. During that time, he was also a part-time clinical lecturer in Birmingham dental school and a member of Sandwell LDC. In 2003 he moved to Mid Wales and worked part-time for the community dental service treating mainly paediatric and special care patients and as an associate dentist in a predominately private practice. In 2009 he became the full-time clinical lead for Powys Teaching Health board. He is currently the Associate Dental Director for PTHB and Deputy Dental Director for Welsh Government. Warren leads Workstream 1, overseeing the finance elements of the Reform Programme.