The intimate coexistence of multiple phases in ferroelectrics has been shown to result in exotic electromechanical properties, such as giant piezoelectricity. Here, via a thickness-driven phase transition, the phase coexistence and enhanced piezoelectricity in a few tens of nanometers thick, Pb-free CaTiO₃ films are demonstrated. Due to the competition between interfacial and bulk energies, as film thickness increases, epitaxial CaTiO₃ films exhibit a ferroelectric-to-paraelectric phase transition that is concomitant with the rhombohedral-to-orthorhombic structural transition. This so-called thickness driven morphotropic phase transition (MPT) in nanoscale CaTiO₃ films stems from the metastable nature of ferroelectricity. The resulting morphotropic phase boundary at the atomic scale in nanoscale CaTiO₃ films is visualized. It is also shown that this thickness-driven MPT can lead to reasonably good piezoelectricity at the nanoscale. This study highlights the rich phase evolution of complex ferroelectrics as a novel platform to control the functionality of nanoscale electromechanical devices.