Precise sensing with as high a performance as possible is desired in fast-paced nanotechnologies. One primary option is plasmonic sensing of a metallic single-particle because of its ability to enhance light–matter interactions at the deep subwavelength scale with extreme spatial accuracy. However, plasmonic sensing suffers from broad resonance linewidths with tremendous metallic damping. Here we find out that the plasmonic linewidths of single gold nanoparticles (NPs) are significantly narrowed for precise sensing. This is realized by coupling a dielectric mirror, i.e., distributed Bragg reflector (DBR), with plasmonic modes of single NPs. Specifically, two types of plasmonic NPs, e.g., nanoplates (NPlts) and nanospheres (NSphs), have been demonstrated with distinctive plasmonic modes. Consequently, the narrowed linewidths are shown to substantially improve the sensing performance, as the sensing figure of merit (FOM) is improved by more than an order of magnitude. This single-particle based plasmonic sensing with narrowed linewidth sheds light on the new mechanism for the sensing nanotechnologies.