Valentine, a citizen of Sierra Leone, is an experienced public servant with valuable knowledge of public administration in Africa that stems from his time in the Government of Sierra Leone. He has a postgraduate diploma in Development Administration from The University of Birmingham and has worked within various government ministries in Sierra Leone since the 1970s. These include positions as the Senior Assistant Secretary and later as the Deputy Secretary within the Ministry of Defence, Ministry of Transport and Communications, and Ministry of Trade and Industry. In 1983 he became the Permanent Secretary within the Office of the President, and later progressed to become Secretary of the Cabinet and then Head of Civil Service.
In April 2000, Valentine was appointed Commissioner of the Anti-Corruption Commission in Sierra Leone. As Commissioner he was responsible for the hiring of all relevant staff, controlling the use of all finances and resources and for implementing the mandate of the commission. This mandate was broad and included investigating and prosecuting offenders of corruption, implementing preventative measures against corruption and involved educating civil society about the damaging effects of corruption in order to instill a sense of responsibility around the issue of corruption. It was through public cooperation and their willingness to report incidences of corruption that the commission was able to tackle corruption cases against high-ranking officials.