Hybrid flow batteries are one of the most promising technologies for storing the electricity generated from intermittent renewables, such as wind and solar. However, most of the existing hybrid systems currently suffer from low power density and poor cycle performance resulted from the parasitic reactions. To mitigate these issues, here we report a tin-iron hybrid flow battery in which the stannous chloride anolyte is separated from the ferric/ferrous chloride catholyte. With the reversible tin metal deposition/stripping and ferric/ferrous chloride redox reactions at carbon surfaces, the present battery delivers an energy efficiency of 78.5% even at the current density of 200 mA cm−2. In addition, owing to high hydrogen overvoltage of metallic tin, the parasitic hydrogen evolution reaction in the negative electrode can be largely avoided so that the battery can stably operate over 700 cycles without obvious efficiency decay. With the excellent rate and cycle performance, it is envisioned that the tin-iron flow battery is a promising candidate for large-scale energy storage applications.