Although Cu possesses many unique advantages for electrocatalytic CO₂ reduction reaction (CO₂RR), it is not suitable for electrosynthesis of urea from CO₂ and NO₃⁻ because of high energy barriers for the formation of *COOH and *CO intermediates and C–N bonds. Herein, Cr₂O₃ nanoparticle (NP)/Cu nanosheet (NS) heterojunction electrocatalysts are reported for highly efficient electrocatalytic co-reduction of CO₂ and NO₃⁻ toward urea production. The strongly coupled heterostructure interface between Cr₂O₃ NPs and Cu NSs exhibits synergistic effect and optimizes the adsorption of intermediates. The resultant heterojunction electrocatalysts could achieve a high urea Faradaic efficiency (FE_urea) of 62% at an ultralow applied potential of 0 V vs. reversible hydrogen electrode (RHE), which is among the best results reported to date. Moreover, the electrocatalysts showed good recycling stability. The in-situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations revealed that the Cr₂O₃ NPs/Cu NSs heterostructure could not only reduce formation energy barriers of *COOH and *CO intermediates but also promote the coupling of *CO and *NH₂ to form C–N bonds, leading to a high FE_urea. This study demonstrates a heterojunction engineering strategy for the rational design of high-performance Cu-based electrocatalysts for urea generation.