Evidence of use of toxic gas chemical weapons in the Syrian war has been reported by governmental and non-governmental international organizations since the war started in March 2011. To date, the profiles of victims of the largest chemical attacks in Syria remain unknown. In this study, we used descriptive epidemiological analysis to describe demographic characteristics of victims of the largest chemical weapons attacks in the Syrian war. We analysed conflict-related, direct deaths from chemical weapons recorded in non-government-controlled areas by the Violation Documentation Center, occurring from March 18, 2011 to April 10, 2017, with complete information on the victim's date and place of death, cause and demographic group. 'Major' chemical weapons events were defined as events causing ten or more direct deaths. As of April 10, 2017, a total of 1206 direct deaths meeting inclusion criteria were recorded in the dataset from all chemical weapons attacks regardless of size. Five major chemical weapons attacks caused 1084 of these documented deaths. Civilians comprised the majority (n = 1058, 97.6%) of direct deaths from major chemical weapons attacks in Syria and combatants comprised a minority of 2.4% (n = 26). In the first three major chemical weapons attacks, which occurred in 2013, children comprised 13%-14% of direct deaths, ranging in numbers from 2 deaths among 14 to 117 deaths among 923. Children comprised higher proportions of direct deaths in later major chemical weapons attacks, forming 21% (n = 7) of 33 deaths in the 2016 major attack and 34.8% (n = 32) of 92 deaths in the 2017 major attack. Our finding of an extreme disparity in direct deaths from major chemical weapons attacks in Syria, with 97.6% of victims being civilians and only 2.4% being combatants provides evidence that major chemical weapons attacks were indiscriminate or targeted civilians directly; both violations of International Humanitarian Law (IHL). Identifying and quantifying chemical weapons violations requires inter-disciplinary collaboration to inform international policy, humanitarian intervention and legal action.