In single-atom catalysts (SACs), the isolated metal atoms on solid support are often charged. Taking advantage of this common feature, we establish ionic liquid-stabilized single-atom catalysts (ILSSACs) employing electrostatic interaction as a general stabilization strategy. While Pt nanoparticles were formed on hydroxyapatite after reaction when unprotected, Pt remained atomically dispersed on ionic liquid-stabilized samples. Density functional theory calculations reveal that the activation energy for the transformation of two isolated Pt atoms to a Pt dimer increases remarkably from 0.11 to 0.72 eV with the protection of [Bmim][BF4]. The presence of ILs also tunes the electronic state of Pt1, inducing an order-of-magnitude hydrogenation activity increase. The simple stabilization strategy is easily extended to SACs comprising various metal atom-support combinations. For instance, ILs significantly improved the stability and selectivity of a Pd1 catalyst for the hydrogenation of acetylene, thus outperforming unprotected SACs.