We have explored the reactivity of diazo compounds under electrochemical conditions to establish a cascade sequence of thiolation/cyclization/reduction reactions. Electrolyzing styryl diazo imides and aryl thiols enables direct access to a single diastereoisomer of 2,5-pyrrolidine-dione-fused thiochromans in good yield under mild and metal-free conditions. Notably, a tunable reactivity has been achieved via S-H insertion at the diazo center in modified reaction conditions. Based on the experimental evidences, including the detection of key intermediates and computational studies, the mechanism for the electrochemical cascade reaction has also been established.