The Tarim Large Igneous Province constitutes the most significant tectono-thermal event in the evolution of the Tarim Craton, forming mafic-ultramafic layered intrusions (e.g., the Wajilitag complex) that host vanadium-titanium magnetite deposits. However, intermediate rocks identified at the margin of the Wajilitag intrusion have been largely overlooked. Thus, the magmatic evolution and deep-seated geodynamic processes of the Tarim Large Igneous Province have been incompletely understood. This study presents a comprehensive investigation of the Wajilitag biotite monzodiorite, integrating detailed petrographic, geochronological, and geochemical analyses. The biotite monzodiorite is primarily composed of plagioclase, orthoclase, biotite, hornblende and augite. LA-ICP-MS zircon U-Pb dating yields an age of 277.9±1.5 Ma (MSWD = 0.85), constraining the emplacement of the biotite monzodiorite in the Early Permian. This age is slightly younger than that of the Wajilitag mafic-ultramafic layered intrusion. The biotite monzodiorite is characterized by relatively low silica (SiO₂content is 52.14%–53.50%) and high alkali contents (Na₂O+K₂O content is 7.26%–7.60%), classifying it as shoshonitic series. The chondrite-normalized REE pattern displays a right-sloping trend with LREE enrichment and HREE depletion. It is enriched in large-ion lithophile elements (LILEs; e.g. Ba and Pb) and possesses high concentrations of high-field-strength elements (HFSEs; e.g. Nb, Ta, Zr, Hf), without Nb-Ta negative anomalies. These geochemical features are indicative of an OIB-like enriched mantle source, with negligible crustal contamination during ascent. The slightly enriched zircon Hf isotopic composition (εHf(t) value range from −1.8 to −4.4) of the Wajilitag biotite monzodiorite is similar to that of continental flood basalts from the Tarim Large Igneous Province. In the TiO₂-MnO-P₂O₅ and Hf-Th-Ta tectonic discrimination diagrams, the rocks exhibit an affinity consistent with within-plate basalts. Integrated studies suggest that the Wajilitag biotite monzodiorite was derived from partial melting of an enriched lithospheric mantle that had been modified by subducted oceanic crust, with eclogite as the residual phase in the source. The interaction between a mantle plume and the subducted slab played a significant role in its formation.