A comparative study of the electrochemical intercalation of Ca2+ and Mg2+ in layered TiS2 using alkylcarbonate-based electrolytes is reported, and for the first time, reversible electrochemical Ca2+ insertion is proved in this compound using both X-ray diffraction and differential absorption X-ray tomography at the Ca L2 edge. Different new phases are formed upon M2+ insertion that are structurally characterized, their amount and composition being dependent on M2+ and the experimental conditions. The first phase formed upon reduction is found to be the result of an ion-solvated intercalation mechanism, with solvent molecule(s) being cointercalated with the M2+ cation. Upon further reduction, new non-cointercalated calcium-containing phases seem to form at the expense of unreacted TiS2. The calculated activation energy barriers for Ca2+ migration in TiS2 (0.75 eV) are lower than those previously reported for Mg (1.14 eV) at the dilute limit and within the CdI2 structural type. DFT results indicate that the expansion of the interlayer space lowers the energy barrier and favors a different pathway for Ca2+ migration. The authors acknowledge funding from Ministerio de Economía y Competitividad (Spain) for magnesium battery research (grant MAT2014-53500R). ICMAB’s authors are also grateful for funding from Toyota Motor Europe for calcium battery research, for support through the “Severo Ochoa” Program for Centres of Excellence in R&D (SEV- 2015-0496), to ALBA synchrotron for beam time allocation at MSPD beamline (proposal 2014070933), and to Dr. François Fauth for his assistance during data collection. The X-ray tomography experiments were performed at MISTRAL beamline at ALBA Synchrotron with the collaboration of ALBA staff, and the ICMAB authors are grateful to Dino Tonti for helpful discussion. M.E.A.-d.D. and N.B. acknowledge computational facilities from Universidad de Oviedo (MALTA-Consolider cluster). Peer reviewed