|In the aftermath of the UN Secretary General’s call for a global ceasefire following the outbreak of COVID-19, a discussion emerged regarding how international humanitarian law applies during a global pandemic. This Article contributes to that discussion through the lens of two distinct strands of thought on the Martens Clause. The first considers the Martens Clause as capable of affecting understandings of how the existing law of armed conflict applies to the conduct of hostilities during a global pandemic. Applying various scholarly and judicial interpretations of the Martens Clause’s contemporary legal import, the Article argues that the humanitarian law principles of proportionality, distinction, and military necessity have significant legal bearing on the conduct of hostilities concurrent to a global pandemic. During a global pandemic, the principle of proportionality ought to insist that military commanders include foresee-able incidental harm to civilians resulting from an attack’s expected impact on disease transmission in their incidental harm calculus. The principle of distinction should mandate that the effects of chosen means and methods of combat—including on disease transmission—be limited to military objectives. And the principle of military necessity obliges respect for its delicate balance with humanity, allowing only that which is necessary to achieve legitimate objectives—including taking seriously the duty to take tailored precautions before attacks amidst a global pandemic. These principles, particularly in light of the Martens Clause’s principles of humanity and the dictates of the public conscience, have important legal sway over the conduct of hostilities during pandemics. The second strand of thought on the Martens Clause relates to its ability in certain limited and defined situations to affect the formation process of new customary rules of humanitarian law. This Article argues that armed conflict during a global pandemic falls into this narrow category and that, as a result, the Martens Clause might influence the formation of an emerging custom regulating armed conflict during a global pandemic. In light of significant international support for the call for a global ceasefire in response to the outbreak of COVID-19, the Article assesses whether a new rule of humanitarian law mandating a ceasefire amidst the outbreak of future global pandemics is forming. Analyzing the current stage of this lex ferenda, the Article illustrates the elements lacking in the formation process. Nonetheless, such a rule solidifying into new customary law in the aftermath of the COVID-19 pandemic would be a normatively positive evolution in light of the threat posed by future pandemics.