The safety of drinking water has a significant impact on human life and health, with the common presence of Pb (II) causing harm to human beings. The physical adsorption method is an effective means of removing Pb (II) from water. In this study, three types of biochar were produced through a one-step process using agricultural and forestry wastes (rape straw, bagasse, and walnut shell) as raw materials and KHCO₃ as a co-carbonization agent. The resulting biochar exhibited remarkable adsorption capacities for Pb (II). The biochar prepared via a single carbonization process demonstrates excellent adsorption performance towards Pb (II). The adsorption capacity of bagasse-derived biochar reaches 76.94 mg/g, which is 4.5-fold higher than that of the control. For walnut shell-derived biochar, the adsorption value attains 124.90 mg/g, representing a 7.5-fold enhancement. Notably, rape straw-derived biochar demonstrates the maximum adsorption capacity, up to 265.69 mg/g. Mechanistic analysis reveals that the adsorption of rape straw biochar is dominated by ion exchange, while also being influenced by physical adsorption, coprecipitation, and electrostatic attraction. Intriguingly, in this study, the sole use of KHCO₃ as a co-carbonization agent remarkably increases the specific surface area of the biochar and facilitates the formation of micropores. Without the need for pre-carbonization, this approach substantially boosts the Pb (II) adsorption capacity of the biochar. This one-step carbonization strategy exhibits distinct operational convenience and cost-effectiveness, providing promising materials for the low-cost removal of Pb (II) in natural water bodies and open environments, while also offering a viable technical route for the fabrication of high-performance biochar for heavy metal remediation.