Materials combining electrically switchable ferroelectricity and tunable topological states hold significant promise for advancing both fundamental quantum phenomena and practical device architectures. Here, we employ first-principles calculations to systematically investigate the sliding ferroelectricity-mediated topological transitions in bilayer $M{\mathrm{Bi}}_2{\mathrm{Te}}_4$ ($M=\mathrm{Ge},\mathrm{Sn},\mathrm{Pb}$) systems. By systematically engineering interlayer sliding configurations with oppositely polarized states, we demonstrate the emergence of reversible band inversion accompanying with topological phase transitions. The obtained topologically nontrivial band gaps can reach up to 31 meV (${\mathrm{GeBi}}_2{\mathrm{Te}}_4$), 36 meV (${\mathrm{SnBi}}_2{\mathrm{Te}}_4$), and 35 meV (${\mathrm{PbBi}}_2{\mathrm{Te}}_4$), respectively, enabling the room-temperature observation of the quantum spin-Hall effect. In particular, these systems exhibit substantial out-of-plane ferroelectric polarization of about 0.571–0.623 pC/m. Two independent signatures unambiguously confirm the topological nontriviality: (i) the resulting $Z{}_2$ topological invariant ${\mathbb{Z}}_2=1$, and (ii) the emergence of gapless helical edge states spanning the bulk insulating gap. This synergy arises from the unique sliding-induced charge redistribution mechanism, which simultaneously modulates the interlayer interaction and breaks the out-of-plane inversion symmetry. The coengineering of nonvolatile ferroelectric switching and topologically protected conduction channels in $M{\mathrm{Bi}}_2{\mathrm{Te}}_4$ bilayers establishes a material paradigm for designing reconfigurable quantum devices, where electronic topology can be electrically controlled via polarization reversal. Our study provides critical insights in manipulating quantum states in van der Waals ferroelectrics for multifunctional nanoelectronics.

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• Edge states
• First-principles calculations
• Spin-orbit coupling
• Topological insulators
• Topological materials