Mr Tan joined the Singapore Police Force in 1983. After receiving his senior officer training at the Police Academy, he did a stint in criminal investigation. Thereafter he served in the Internal Security Department handling investigations into matters of national security concern. In 1998, he was seconded to the Singapore Immigration & Registration as its Deputy Director. In 2001, he was seconded to the Central Narcotics Bureau first as its Deputy Director and thereafter to head the CNB as its youngest Director. In 2005, he became the Commissioner of the Immigration & Checkpoints Authority. On 1 October 2010, the President of Singapore appointed him as the Director of the Corrupt Practices Investigation Bureau.