Autophagy plays a complex role in cancer progression, serving as both a tumor suppressor and a promoter, depending on the context. In triple-negative breast cancer (TNBC), a particularly aggressive subtype with limited therapeutic options, autophagy inhibition has emerged as a promising strategy to enhance the efficacy of chemotherapy. This study investigates the synergistic effects of autophagy suppression using LC3 siRNA-loaded “smart” nanoparticles (LC3siRNA-NPs) in combination with doxorubicin (DOX) to overcome chemoresistance in TNBC. We engineered a well-defined copolymer, poly[hexyl methacrylate-co-2-(dimethylamino) ethyl methacrylate-co-trimethylaminoethyl methacrylate iodide], and a PEG heteroarm beta-cyclodextrin (βCD) core star copolymer that delivers LC3 siRNA, effectively silencing the autophagy-related gene LC3. In vitro, the coadministration of LC3siRNA-NPs and DOX significantly inhibited TNBC cell proliferation, migration, and colony formation, while inducing apoptosis more effectively than either treatment alone. Mechanistically, this combination downregulated key oncogenic markers such as PARP, cyclin D1, and Src, enhancing the therapeutic outcome. In vivo, treatment with LC3siRNA-NPs and DOX in a TNBC xenograft model resulted in superior tumor growth suppression compared to that with monotherapy alone. Our findings highlight the potential of autophagy-targeting nanocarriers to improve chemotherapy outcomes and provide an effective approach to TNBC treatment by enhancing chemotherapeutic sensitivity and reducing tumor resistance.