Selective CO2 photoreduction to value‐added multi‐carbon (C2+) feedstocks, such as C2H4, holds great promise in direct solar‐to‐chemical conversion for a carbon‐neutral future. Nevertheless, the performance is largely inhibited by the high energy barrier of C–C coupling process, thereby leading to C2+ products with low selectivity. Here we report that through facile surface immobilization of a 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIM‐BF4) ionic liquid, plasmonic Cu nanowires could enable highly selective CO2 photoreduction to C2H4 product. At an optimal condition, the resultant plasmonic photocatalyst exhibits C2H4 production with selectivity up to 96.7% under 450 nm monochromatic light irradiation, greatly surpassing its pristine Cu counterpart. Combined in situ spectroscopies and computational calculations unravel that the addition of EMIM‐BF4 ionic liquid modulates the local electronic structure of Cu, resulting in its enhanced adsorption strength of *CO intermediate and significantly reduced energy barrier of C–C coupling process. This work paves new path for Cu surface plasmons in selective artificial photosynthesis to targeted products.