Sustainable Happiness or Exploitative Happiness? A Global Justice Perspective on Cross‐Border Spillover Effects

National happiness levels are often attributed to domestic environmental and socioeconomic conditions or policies, yet how one country's pursuit of happiness affects others through global trade remains underexplored. This study adopts a global justice lens to examine negative spillover effects—harmful environmental and social impacts that countries impose on others via transnational supply chains and production networks. Using cross‐sectional global data for 2019 and 2024, the analyses reveal a growing concentration of spillovers, particularly from advanced economies toward more developing ones. The findings show that higher national happiness scores are frequently accompanied by greater negative spillovers, which also indirectly reduce other countries' happiness by amplifying air pollution (PM2.5). This pattern reflects a global trend of “exploitative happiness” rather than “sustainable happiness.” The study highlights the limitations of current governance mechanisms in managing cross‐border supply chains and calls for transparent data sharing, robust transnational regulatory frameworks, and transformative shifts in public awareness and degrowth‐oriented lifestyles to achieve forms of happiness that do not exploit other people or the environment.