Bassem Mirhaj al-Hassan obtained a doctorate in sociology from Damascus University, where he began to oversee Unit 450 under the Scientific Research Institute. Al-Hassan was responsible for protecting chemical weapons in Syria. In 2008, he was appointed head of the Security and Military Office in the Republican Palace and special strategic military adviser to Assad. During his work at the Republican Palace, Bassam al-Hassan was implicated in numerous crimes against the Syrian people, especially those involving chemical weapons.

Al-Hassan was one of the most prominent officials directly responsible for the chemical humanitarian and war crimes committed by the regime, as he was responsible for passing military orders from the Republican Palace to the units and sectors specialized in their use. There have been 221 uses of chemical weapons documented since the first attack, recorded in December 2012 until April 2018 when the regime launched a chemical attack against the city of Douma in eastern Ghouta. These attacks have claimed the lives of over 1,460 people.