AbstractPotassium‐ion batteries (PIBs) offer a cost‐effective and resource‐abundant solution for large‐scale energy storage. However, the progress of PIBs is impeded by the lack of high‐capacity, long‐life, and fast‐kinetics anode electrode materials. Here, we propose a dual synergic optimization strategy to enhance the K+ storage stability and reaction kinetics of Bi2S3 through two‐dimensional compositing and cation doping. Externally, Bi2S3 nanoparticles are loaded onto the surface of three‐dimensional interconnected Ti3C2Tx nanosheets to stabilize the electrode structure. Internally, Cu2+ doping acts as active sites to accelerate K+ storage kinetics. Various theoretical simulations and ex situ techniques are used to elucidate the external–internal dual synergism. During discharge, Ti3C2Tx and Cu2+ collaboratively facilitate K+ intercalation. Subsequently, Cu2+ doping primarily promotes the fracture of Bi2S3 bonds, facilitating a conversion reaction. Throughout cycling, the Ti3C2Tx composite structure and Cu2+ doping sustain functionality. The resulting Cu2+‐doped Bi2S3 anchored on Ti3C2Tx (C‐BT) shows excellent rate capability (600 mAh g–1 at 0.1 A g–1; 105 mAh g–1 at 5.0 A g–1) and cycling performance (91 mAh g–1 at 5.0 A g–1 after 1000 cycles) in half cells and a high energy density (179 Wh kg–1) in full cells.