The success of DUNE’s MeV physics program depends upon high-precision knowledge of the charged-current (CC) ${\nu }_e+{}^{40}Ar$ cross section. While there are indirect constraints on the cross section with uncertainties at the $$10% level, the only direct measurement in the MeV range disagrees by more than a factor of two. We show, surprisingly, that the cross section can be precisely measured using the solar-neutrino data themselves. This is possible because of independent knowledge of the ${}^8$B flux and survival probability, plus the distinctive angular distributions of the Fermi and Gamow-Teller transitions that comprise the cross section. We propose new methods to extract the transition strengths, considering both intuitive groupings and a Principal Component Analysis. Assuming pessimistic detection performance but controlled detector systematic uncertainties, we demonstrate that a precision of $$2% on the cross section can be achieved in the 9–15~MeV energy range. These results will be an important foundation for studying the cross section up to several tens of MeV, where the complexity increases significantly due to nuclear breakup channels but where reducing uncertainties is critical for supernova and atmospheric neutrino studies.