[Background] Magnetic nanoparticle-mediated isolation (MMI) is a culture-independent approach for identifying active degraders from complex microbial communities. However, there are few studies about the MMI-based identification of active bacteria involved in the degradation of recalcitrant 3,3',4,4'-tetrachlorobiphenyl (PCB77). [Objective] To isolate active PCB77 degraders from soil and assess the pollutant degradation capacity. [Methods] Magnetic nanoparticles (MNPs) were used to enrich the active PCB77 degraders in soil. The change in bacterial community composition was determined by high-throughput sequencing. A PCB77 degrader was isolated from MNP-enriched culture, and its performance of degrading polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) was assessed. [Results] The MNP-enriched culture was capable of degrading PCB77 with high efficiency compared with the control, which increased from 6% to 79.3%. The treatment with MNPs decreased the bacterial diversity and changed the community composition. PCB-degrading Rhodococcus sp. CT2 and Paenibacillus sp. MT2 were isolated from the control and MMI culture, respectively. Rhodococcus was dominant in the control group, while the dominant degraders included both Rhodococcus and Paenibacillus in the MMI group. The strain MT2 degraded 65.2% of PCB77 serving as the sole carbon source, and this degradation rate was close to that in MNP-enriched culture and significantly higher than that (26.3%) of strain CT2 under the same condition. In addition, the performance of Paenibacillus sp. MT2 in degrading PCBs and PBDEs was better than that of Rhodococcus sp. CT2. [Conclusion] MMI is a powerful approach to enrich active PCB77 degraders from complex microbial communities, with which Paenibacillus sp. MT2 having high PCB degradation efficiency was isolated. The study lays a theoretical basis for developing efficient approaches to remediate the soil contaminated by PCBs.