Polycrystalline In₂Ge₂O₇ with a monoclinic structure (thortveitite-type, T-type) and a cubic structure (pyrochlore-type, P-type) have been synthesized by using different methods. The structural stabilities and electrical transport properties of these two polymorphs under high pressure have been investigated by angle-dispersive X-ray diffraction (ADXRD) and alternate current (AC) impedance spectra. An irreversible structural phase transition from monoclinic (C2/m) to another monoclinic (P2₁/c) phase has been found in the T-type In₂Ge₂O₇ above 6.6 GPa. Furthermore, the pressure dependent electrical resistance of the T-type In₂Ge₂O₇ shows a dramatic change at 5.3 GPa, where it can be attributed to the observed pressure-induced structural phase transition. On the contrary, the P-type In₂Ge₂O₇ with the cubic (Fdm) structure at high pressure is much more stable up to 26.5 GPa.