Ionic liquids are appropriate candidates for the absorption of acid gases such as SO₂. Six anion functionalized ionic liquids with different basicities have been studied for SO₂ absorption capacity by employing quantum chemical calculations and molecular dynamics (MD) simulations. Gas phase quantum calculations unveil that the high uptake of SO₂ in these ionic liquids originates from the basicity of the anions and the consequent enhanced anion-SO₂ interactions. MD simulations of SO₂–IL mixtures reveal the crucial role of both cations and anions in SO₂ dissolution. Multiple-site interactions of SO₂ with the anions have been identified. The calculated solvation free energy substantiates these observations. The order of computed Henry’s law constant values with change in the anion is in fair agreement with experimentally determined SO₂ solubility order.