Cell shrinkage is an incipient hallmark of apoptosis and is accompanied by potassium release that decreases the concentration of intracellular potassium and regulates apoptotic progression. The plasma membrane K⁺channel recruited during apoptosis has not been characterized despite its importance as a potential therapeutic target. Here we provide evidence that two-pore domain K⁺ (K_2P) channels underlie K⁺ efflux during apoptotic volume decreases (AVD) in mouse embryos. These K_2P channels are inhibited by quinine but are not blocked by an array of pharmacological agents that antagonize other K⁺ channels. The K_2P channels are uniquely suited to participate in the early phases of apoptosis because they are not modulated by common intracellular messengers such as calcium, ATP, and arachidonic acid, transmembrane voltage, or the cytoskeleton. A K⁺channel with similar biophysical properties coordinates regulatory volume decreases (RVD) triggered by changing osmotic conditions. We propose that K_2P channels are the pathway by which K⁺ effluxes during AVD and RVD and that apoptosis co-opts mechanisms more routinely employed for homeostatic cell volume regulation.