  We measure the lifetime of the $D_s^+$ meson using a data sample of 207
fb$^{-1}$ collected by the Belle II experiment running at the SuperKEKB
asymmetric-energy $e^+ e^-$ collider. The lifetime is determined by fitting the
decay-time distribution of a sample of $116\times 10^3$
$D_s^+\rightarrow\phi\pi^+$ decays. Our result is $\tau^{}_{D^+_s} = (499.5\pm
1.7\pm 0.9)$ fs, where the first uncertainty is statistical and the second is
systematic. This result is significantly more precise than previous
measurements.
