Enhancing charge separation in semiconductor photocatalysts is a major challenge for efficient artificial photosynthesis. Herein, a compact heterojunction is designed by embedding half‐metallic C(CN)₃ (hm‐CN) hydrothermally in BiOBr (BOB) as the backbone. The interface between hm‐CN and BOB is seamless and formed by covalent bonding to facilitate the transmission of photoinduced electrons from BOB to hm‐CN. The transient photocurrents and electrochemical impedance spectra reveal that the modified composite catalyst exhibits a larger electron transfer rate. The photocatalytic activity of hm‐CN/BOB increases significantly as indicated by a CO yield that is about four times higher than that of individual components. Density‐functional theory calculations verify that the heterojunction improves electron transport and decreases the reaction energy barrier, thus promoting the overall photocatalytic CO₂ conversion efficiency. The half‐metal nitride coupled semiconductor heterojunctions might have large potential in artificial photosynthesis and related applications.