Epitaxially grown ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ thin films show resistance modulations induced by the inverse piezoeffect of the employed $\mathrm{Pb}\left({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}\right){\mathrm{O}}_3\text{-}{\mathrm{PbTiO}}_3\left(001\right)$ (PMN-PT) substrates. The in-plane strain state of the films can continuously be tuned by application of a piezovoltage to PMN-PT. The lattice deformation of a PMN-PT(001) substrate was quantified by x-ray measurements under an electric field. Variation of in-plane lattice parameters by $\sim 0.06\%$ reversibly changes the resistance of the manganite films by up to 9% at 300 K and shifts the magnetic Curie temperature. Films of different thicknesses from 50 to 290 nm, offering different as-grown strain states, have been studied.