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Biochar has been widely recognized as an environmentally efficient adsorbent for removal of heavy metals in wastewater. However, inferior adsorption capacity limits its practical application. In this study, a H3PO4–modified tea branch biochar (PTBB) was firstly prepared through the one step pyrolysis of H3PO4-pretreated tea branch powder for enhancing removal efficiency of Cd2+and Pb2+from aqueous solutions. H3PO4modification altered the physicochemical properties of pristine biochar. The PTBB exhibited superior adsorption performance. Its maximum adsorption capacities of Cd2+and Pb2+were 98.25 mg g−1and 127.5 mg g−1at the pH 6 and dosage of 2 g L−1, which was 1.5 and 1.3 folds of the pristine biochar, respectively. Cd2+and Pb2+adsorption data by PTBB were well fitted by the Langmuir isothermal and pseudo-second order kinetic models, indicating monolayer chemical adsorption controlled the adsorption process. The adsorption of Cd2+and Pb2+by PTBB was a spontaneous endothermic process and less affected by coexisting cations. PTBB demonstrated a greater affinity for Pb2+as compared with Cd2+in binary metal systems. Moreover, PTBB could maintain good stability and regeneration properties. The adsorption of Cd2+and Pb2+by PTBB was attributed to cation exchange, precipitation, complexation, and π electron interactions. The quantitative analysis indicated that complexation and precipitation were the primary adsorption mechanisms, which accounted for 50.52–50.56% and 36.7–42.18% to total Cd2+and Pb2+adsorption for PTBB, respectively. Therefore, PTBB exhibits great potential for application in the remediation of wastewater containing Cd2+or Pb2+.