Direct data processing in nonvolatile memories can enable area- and energy-efficient computation, unlike independent performance between separate processing and memory units; repetitive data transfer between these units represents a fundamental performance limitation in modern computers. Spatially mobile conducting domain walls in ferroelectrics can be redirected between drain, gate, and source electrodes to function as nonvolatile transistors with superior energy efficiency, ultrafast operating and communication speeds, and high logic/storage densities. Here, we demonstrate in-memory computing using multilevel domain wall diodes at LiNbO₃ interfaces. Ultrathin domains within interfacial layers between each mesa-like memory cell and the contactelectrodes can rectify diode-like domain wall currents with on/off current ratios exceeding 10⁷at low operating voltages, surpassing the performance of traditional p-n junctions using built-in potentials across depletion layers. NOT, NAND, and NOR gate logic functions are demonstrated, providing insights into high-density integration of multilevel storage and computational units in all-ferroelectric domain wall devices.