We search for $CP$ violation in the charged charm meson decay ${D}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}$, based on a data sample corresponding to an integrated luminosity of $921\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the Belle experiment at the KEKB ${e}^{+}{e}^{\ensuremath{-}}$ asymmetric-energy collider. The measured $CP$-violating asymmetry is $[+2.31\ifmmode\pm\else\textpm\fi{}1.24(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.23(\mathrm{syst})]%$, which is consistent with the standard model prediction and has a significantly improved precision compared to previous results.