A branching fraction measurement of the $B0\to Ds+\pi -$ decay is presented using proton-proton collision data collected with the LHCb experiment, corresponding to an integrated luminosity of $5.0$fb$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$. The branching fraction is found to be $B(B0\to Ds+\pi -)=(19.4\pm 1.8\pm 1.3\pm 1.2)\times 10-6$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the $B0\to D-\pi +$, $Ds+\to K+K-\pi +$ and $D-\to K+\pi -\pi -$ branching fractions. This is the most precise single measurement of this quantity to date. As this decay proceeds through a single amplitude involving a $b\to u$ charged-current transition, the result provides information on non-factorisable strong interaction effects and the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $Vub$. Additionally, the collision energy dependence of the hadronisation-fraction ratio $fs/fd$ is measured through $B¯s0\to Ds+\pi -$ and $B0\to D-\pi +$ decays.