Localized tumor photothermal cancer ablation is a minimally invasive therapeutic modality for combating cancer, but it often suffers from low therapeutic efficacy and poor precision due to the poor accumulation and non-uniform distribution of used photothermal-conversion agents in tumor tissue via the typical intravenous administration. To address this, an injectable and phase-changeable composite bio-injection consisting of biocompatible two-dimensional (2D) niobium carbide (Nb2C) MXene and the plant-originating protein, zein, has been engineered for near infrared (NIR)-II-triggered tumor photothermal ablation. Zein can respond to aqueous microenvironments and also external photo-triggers from the NIR-II bio-window (1064 nm), and transforms into a solid bio-implant after solvent exchange between ethanol and water. Which, thus, traps Nb2C MXene and heat, improving ablation efficiency and enabling the precise and complete eradication of 4T1 breast tumor cells without additional safety concerns. More significantly, shear wave elastography (SWE) as a deep-penetration imaging mode that can reflect the ablated outcomes via monitoring tissue density variation, has been employed to guide the photo-thermal ablation process to further improve the ablation precision. Thus, this compatible and phase-changeable bio-injection capable of improving photo-thermal ablation efficiency holds great potential in clinical applications.