Exotic cluster radioactivity is proposed to constrain neutron skin thickness of $^{208}\mathrm{Pb}$ and the density slope of symmetry energy $L({\ensuremath{\rho}}_{0})$. Based on the density-dependent cluster model (DDCM) with the M3Y effective nucleon-nucleon interaction, the neutron skin thickness of $^{208}\mathrm{Pb}$ is closely related to the density slope $L({\ensuremath{\rho}}_{0})$ where the cluster radioactivity serves as a link between them. The single-nucleon potential constructed from the M3Y nucleon-nucleon interaction, especially its isovector part, is found to be particularly important in determining the neutron skin in a finite nucleus and the density slope parameter $L({\ensuremath{\rho}}_{0})$ in nuclear matter. The correlation between the neutron skin thickness of $^{208}\mathrm{Pb}$ and the density slope parameter is obtained from cluster radioactivity where the standard Fermi-form density parameterizations and the standard M3Y effective interactions are assumed in DDCM.