Materials with an abrupt transition between a low and a high thermal conductance state at a critical temperature would be useful for thermal regulation applications. Here, the authors report a high contrast reversible thermal conductivity change through the thermally-induced martensitic transition (MT) in Ni-Mn-In alloys. The authors measure the thermal conductivity of a wide temperature range 130 < T < 530 K using time-domain thermoreflectance (TDTR). The thermal conductivity of these alloys increases from approximate to 7.0-8.5 W m(-1) K-1 to approximate to 11.5-13.0 W m(-1) K-1 through the MT near 300 K as temperature rises, with a rate of change among the highest yet reported in solid-state materials with thermally-induced phase transitions. Based on Hall resistivity measurements, the authors further show that the change of thermal conductivity is dominated by the electronic contribution, which results from a unique carrier mobility change through the MT. Their findings highlight the interplay between the structural disorders and the thermal transport in alloys through solid-state phase transitions and open a new avenue in the search of high-performance materials for thermal regulation.