Tin is a critical and rare metal produced via carbothermic reduction smelting of upgraded concentrates in two steps, primary and secondary reduction. There is limited literature available on cassiterite smelting and the thermodynamic behavior of Sn during primary and secondary reduction processes. The present work performs a systematic assessment/optimization of smelting parameters of a simplified cassiterite concentrate for the first time. This assessment was carried out with the aid of thermochemical analysis. The effect of process variables including reduction extent, temperature, and flux addition on the outputs of the primary and secondary reduction steps was studied. The effects of temperature and slag composition on slag liquidus temperature and viscosity were determined. The effect of recycling the process by-product, the hard head (HH), on operational parameters and outcomes, especially Sn recovery, was also investigated, and a series of optimum process conditions was proposed.