David St John Barnett was born in Linstead St. Catherine Jamaica. He commenced his Service in Law Enforcement when he joined the Jamaica Constabulary Force (JCF) January 3, 2006, where he gave selfless service for 11yrs and 8mnths, he left the JCF at the Rank of Detective Sergeant. During his tenure there he along with Mark Tomlinson, Oneil McKenzie, Howard Shand led the modernization to revolutionize the Jamaica Police Academy now National Police College of Jamaica recruitment system named Recruitment Management Information System (RMIS 1.0) which saw all application being proceed electronically. He served with Special Branch now National Intelligence Bureau (NIB) in all his service with the JCF.

Barnett left the JCF and took up an offer with the Royal Turks and Caicos Islands Police Force RT&CIPF in August of 2017. He currently serves as a Detective Constable. On March 19, 2019 he was elected to serve the Police Welfare Association (PWA). He campaigned on the slogan Reliable Effective Authentic Loyal "REAL Change". He was elected by his peers to serve as Chairman upon their first meeting. Barnett is the first ever Constable in the history of the RT&CIPF to hold the position of Chairman.

He is said to be a dedicated worker who prides himself in ensuring the welfare of all Rank and File members of the RT&CIPF are taken care of. Since assuming Officer April 1, 2019, Barnett is hellbent on keeping his commitment for REAL Change. He has developed the PWA website and integrated his organization with social media. He has implemented an Officer of the month programme, a weekly shout-out for all Officers and a "Did you know?" feature to Encourage, Enlighten, Educate and Empower his members. He has also introduce a contribution scheme to better assist members, he also presided over drafting of a new PWA Constitution and Completed a Police Welfare Fund Rule to govern the contribution scheme. His administration is currently looking for better insurance coverage for their members.