  We report a measurement of the radiative lifetime of the $5s5p \;
{}^{\rm{3}}P^{\rm{o}}_{\rm{0}}$ metastable state in ${}^{87}$Sr, which is
coupled to the 5$s^{\rm{2}} \;$ ${}^{\rm{1}}S_{\rm{0}}$ ground state via a
hyperfine-induced electric dipole transition. The radiative lifetime is
determined to be 151.4(48) s, in good agreement with theoretical results. Our
approach relies on accurate measurements of laser intensity and free-space Rabi
frequency, enabling lifetime measurements of any excited state and particularly
suitable for long-lived states.
