The unique electronic and crystal structures driven by external pressure in transition metal chalcogenides (TMCs) can host emergent quantum states. Here we report pressure-induced metallization, nontrivial $Z_2$ band topology, and superconductivity in TMC ${\mathrm{Ta}}_2{\mathrm{Ni}}_3{\mathrm{Te}}_5$. Our electrical transport measurements show that the metallization emerges at 3.3 GPa, followed by appearance of the superconductivity at $P_{\mathrm{c}}=21.3\mathrm{GPa}$ with $T_{\mathrm{c}}\sim 0.4\mathrm{K}$. Room-temperature synchrotron x-ray-diffraction experiments demonstrate the stability of the pristine orthorhombic structure upon compression. Our first-principles calculations further reveal a topological phase transition (from $Z_2=0$ to $Z_2=1$), which occurs after ${\mathrm{Ta}}_2{\mathrm{Ni}}_3{\mathrm{Te}}_5$ is turned into an electron-hole compensated semimetal by pressure. The pressure-induced superconductivity at $P_{\mathrm{c}}$ could be attributed to the abruptly enhanced density of states at the Fermi level. These findings demonstrate that ${\mathrm{Ta}}_2{\mathrm{Ni}}_3{\mathrm{Te}}_5$ is a new platform for realizing exotic quantum phenomena in TMCs as well as exploring the interplay between topological property and superconductivity.

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• Pressure effects
• Superconductivity
• Topological phase transition
• Layered semiconductors
• Topological materials
• First-principles calculations
• Pressure techniques