Lead (Pb) is among the most severe and hazardous heavy metal pollutants. However, the complex response and detoxification mechanisms employed by insects to counteract Pb exposure remain incompletely elucidated. Using Drosophila melanogaster as a model, we integrated Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), transcriptomic analysis, Drosophila genetic tools, and a series of physiological assays to systematically investigate the signaling networks underlying the insect Pb detoxification response. Our findings revealed that Pb accumulation in D. melanogaster followed a nonlinear pattern with increasing dietary Pb concentration. Further mechanistic exploration demonstrated that Pb-induced high expression of Metallothioneins (Mtns), especially the MtnB, directly accelerated Pb excretion, thereby restricting the body’s Pb burden and ultimately contributing to the nonlinear accumulation pattern. To validate this role, we employed an optogenetically controlled bacterial system to drive MtnB expression specifically in the Drosophila midgut; this manipulation effectively suppressed Pb accumulation in the flies and mitigated Pb-induced toxicity. At the molecular level, Pb exposure significantly elevated ROS levels in the Drosophila midgut. This ROS burst subsequently induced Mtns expression through the concerted action of the MTF-1, Nrf2, and JNK signaling pathways. Notably, we observed that Pb exposure activated the Nrf2 pathway via oxidative stress, thereby conferring cross-resistance to pesticides in fruit flies. Collectively, these insights provide a novel perspective on the crosstalk between oxidative stress, metal metabolism, and detoxification systems in insects. They not only advance our understanding of how insects cope with metal toxicity but also highlight the broader environmental implications of metal pollution in ecological systems.