  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
GPa with $T_{\mathrm{c}} \sim$ 0.4 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.
