This study examines the impacts of El Niño–Southern Oscillation on the frequency, duration, magnitude, and timing of heat waves (HWs) in the Indochina Peninsula during 1979–2017. It is found that preceding winter El Niño (La Niña) events prominently amplify (weaken) the HWs in most areas of Indochina by increasing (decreasing) the occurrence of HW events and the number of participating HW days, prolonging (shortening) the duration, and elevating (reducing) the amplitude of such events. These influences are even stronger for severe HWs (i.e., longest and hottest events) than for regular ones with average duration and intensity. Further examinations show that the atmospheric circulation during El Niño events is featured by a weakened Walker circulation that is characterized by an anomalously sinking motion over the western North Pacific (WNP) and Asia and a rising motion over the eastern tropical Pacific. The anomalous subsidence over WNP/Asia is accompanied by suppressed precipitation, and the WNP anticyclone is also enhanced and moves more westward. These patterns are in accordance with the atmospheric controls of HWs in Indochina, thereby favoring the occurrence and sustenance of HW events in the peninsula. La Niña event causes the mostly opposite changes of El Niño, thus inhibiting the HW activities in Indochina.