In this study, the feasibility and mechanism of Pb²⁺ and malachite green (MG) adsorption from wastewater using KMnO₄-modified bamboo biochar (KBC) was evaluated. The KBC was characterized by SEM–EDS, XRD, FTIR and XPS. The adsorption results for Pb²⁺ conformed to pseudo-second-order kinetics and the Langmuir model theory. Unlike the case for Pb²⁺, the Freundlich model better described the adsorption behaviour of MG, indicating that adsorption occurred within multiple molecular layers. Both pseudo-first-order kinetics and pseudo-second-order kinetics fit the MG adsorption data well, indicating that physical adsorption was involved in the adsorption process. In addition, the maximum adsorption capacity for Pb²⁺/MG was 123.47/1111.11 mg·g⁻¹, KBC had high adsorption capacities for Pb²⁺ and MG, and the mechanisms of Pb²⁺ adsorption were mineral precipitation, functional group complexation, and cation-π interactions, while the main mechanisms for MG adsorption were pore filling, π–π interactions, and functional group complexation. In this study, KMnO₄-modified biochar was prepared and used as an efficient adsorbent, and showed good application prospects for treatment of wastewater containing MG and Pb²⁺.