Three thiospinel phases of the In2S3−SnS−SnS2 system solid solution domain have been selected for electrochemical lithium insertion and local investigation by means of 119Sn Mossbauer spectroscopy. Two distinct insertion mechanisms, characterized by two plateaus, are evident from the obtained discharge curves. Mossbauer spectroscopy and X-ray diffraction results are consistent with this. The first insertion mechanism is characterized by the reduction of SnIV and a cell expansion while the second one leads to an increased metallic-type Sn/Li interaction and a cell contraction, both accompanied by a migration of indium from tetrahedral to octahedral sites. The evolution of the hyperfine parameters is discussed to characterize the main differences between the three phases in terms of local and global guest−host interactions.