Ahsan worked as an Assistant Engineer at the Bangladesh Rural Electrification Board before joining the Ministry of Foreign Affairs of Bangladesh as an Assistant Secretary in 1988. In his first diplomatic assignment, from 1992 to 1995, he served as Second Secretary and First Secretary at Bangladesh Embassy in Beijing, China. From 1995 to 1999, he served at Bangladesh High Commission in
London, United Kingdom initially as First Secretary and later as Counsellor. At headquarters in Dhaka from 1999 to 2001, he served as Director (Personnel), Director (
South Asia and SAARC) and Director (Foreign Secretary's Office). Kamrul Ahsan represented Bangladesh at different international negotiations. He was in the drafting group for
Least Developed Countries (LDCs) during the Framework Convention on Climate Change Meetings in Geneva. He was Bangladesh delegate to the
International Maritime Organization from 1996 to 1999. He attended the IISS Shangri La Dialogue, Asia's premier security summit, at Singapore from 2008 to 2012. He also helped to form Bangladesh Business Chamber of Singapore. ==Honours==