Bulk liquid metals (LMs) are unique stimulus-responsive dynamic materials that are appealing across different fields of science and technology, including catalysis. However, the low surface-to-volume ratio, limited atomic-scale design, and required ad-hoc reactor engineering of bulk LM limit their exploitation. Colloidal LM nanoparticles (NPs) can address all of these shortcomings; however, their synthetic chemistry is challenging and less advanced compared to other materials. Here, we advance the synthetic knowledge on LM NPs and propose a colloidal approach for the synthesis of monodispersed In–Ga NPs with tunable indium content via a balanced precursor reactivity strategy. The synthesis generates temperature- and voltage-responsive supercooled metastable NPs, which we leverage for CO2 electroreduction. The metastable NPs show a unique temperature-dependent modulation of active sites, which results in increasing formate production with temperature. This behavior opposes the temperature deactivation reported so far for solid CO2RR catalysts toward the same product.