Li7La3Zr2O12 is considered to be a promising solid electrolyte for all-solid-state batteries. The problem of the poor wettability of Li7La3Zr2O12 by metallic Li can be solved by using Li-In alloys as anode materials. Li-In alloys with different Li contents (40–90 at%) were prepared by an in situ method and investigated in symmetric cells with a Li7La3Zr2O12-based solid electrolyte. The interface resistance between the Li-In alloy (90 at% Li) and solid electrolyte is equal to ~11 Ω cm2 at 200 °C. The cells with 80–90 at% Li in the Li-In anode show stable behavior during cycling with an applied current of ±8 mA (40 mA cm−2). No degradation of the Li7La3Zr2O12-based solid electrolyte in contact with the lithium–indium alloy was observed after galvanostatic cycling. Therefore, the Li-In alloy obtained by our in situ method can be applied as an anode material with Li7La3Zr2O12-based solid electrolyte in lithium power sources.