Heteroepitaxial coupling at complex oxide interfaces presents a powerful tool for engineering the charge degree of freedom in strongly correlated materials, which can be utilized to achieve tailored functionalities that are inaccessible in the bulk form. Here, the charge‐transfer effect between two strongly correlated oxides, Sm0.5Nd0.5NiO3 (SNNO) and La0.67Sr0.33MnO3 (LSMO), is exploited to realize a giant enhancement of the ferroelectric field effect in a prototype Mott field‐effect transistor. By switching the polarization field of a ferroelectric Pb(Zr,Ti)O3 (PZT) gate, nonvolatile resistance modulation in the Mott transistors with single‐layer SNNO and bilayer SNNO/LSMO channels is induced. For the same channel thickness, the bilayer channels exhibit up to two orders of magnitude higher resistance‐switching ratio at 300 K, which is attributed to the intricate interplay between the charge screening at the PZT/SNNO interface and the charge transfer at the SNNO/LSMO interface. X‐ray absorption spectroscopy and X‐ray photoelectron spectroscopy studies of SNNO/LSMO heterostructures reveal about 0.1 electron per 2D unit cell transferred between the interfacial Mn and Ni layers, which is corroborated by first‐principles density functional theory calculations. The study points to an effective strategy to design functional complex oxide interfaces for developing high‐performance nanoelectronic and spintronic applications.