Realizing highly efficient and selective electrochemical CO₂ reduction by using cost-effective catalysts is a key to the large-scale commercialization of this technology. In this work, a nanoporous amalgam catalyst with a tuneable amount of Ag–Hg bonding sites has been developed for selective CO₂ electroreduction to formate or CO via a one-step wet-chemistry method. This catalyst is composed of a Ag(Hg) solid solution phase and a Ag–Hg intermetallic compound, exhibiting a loosened nanorod-channel network morphology. The Ag₇₀Hg₃₀ alloy drives efficient formate generation with a high faradaic efficiency of 85% at a moderate overpotential of 790 mV while the Ag₉₁Hg₉ alloy promotes CO₂ reduction to CO with a faradaic efficiency of 58% at a low overpotential of 590 mV. The switchable product selectivity has been correlated with preferable formation of HCOO* or *COOH intermediates at Ag–Hg and Ag–Ag bonding sites. This work highlights amalgams as novel electrocatalysts for CO₂ reduction to valuable products on demand.