The practical viability of high-energy-density lithium–sulfur (Li–S) batteries stipulates the use of a high-loading cathode and lean electrolyte. However, under such harsh conditions, the liquid–solid sulfur redox reaction is much retarded due to the poor sulfur and polysulfides utilization, leading to low capacity and fast fading. Herein, a self-assembled macrocyclic Cu(II) complex (CuL) is designed as an effective catalyst to homogenize and maximize the liquid-involving reaction. The Cu(II) ion coordinated with four N atoms features a planar (Formula presented.) hybridization, showing a strong bonding affinity toward lithium polysulfides (LiPSs) along the (Formula presented.) orbital via steric effects. Such a structure not only lowers the energy barrier of the liquid–solid conversion (Li2S4 to Li2S2) but also guides a 3D deposition of Li2S2/Li2S. As such, with a 1 wt% electrolyte additive of CuL, a high initial capacity of 925 mAh g−1 and areal capacity of 9.62 mAh cm−2 with a low decay of 0.3%/cycle can be achieved under a high sulfur loading of 10.4 mg cm−2 and low electrolyte/sulfur ratio of 6 µL mgs−1. This work is expected to inspire the design of homogenous catalysts and accelerate the uptake of high-energy-density Li–S batteries.