Hydrogen (H2) therapy has demonstrated antitumor effect, but the therapeutic efficacy is restricted by the low solubility and nontarget delivery of H2. Electrolysis of H2O by electrocatalysts sustainably releases enormous amounts of H2 and inspires the precise delivery of H2 for tumor therapy. Herein, manganese‐doped Ni2S3 nanoelectrodes (MnNi2S3 NEs) are designed for the electrocatalytic delivery of H2 and the activation of antitumor immunity to effectively potentiate H2‐immunotherapy. Ni atoms featuring empty 3d orbitals reduce the initial energy barrier of the hydrogen evolution reaction (HER) by promoting the adsorption of H2O. Moreover, Mn atoms with different electronegativity modulate the electronic structure of Ni atoms and facilitate the desorption of the generated H2, thus enhancing the HER activity of the MnNi2S3 NEs. Based on the high HER activity, controllable delivery of H2 for electrocatalytic hydrogen therapy (EHT) is achieved in a voltage‐dependent manner. Mechanistically, MnNi2S3 NE‐mediated EHT induces mitochondrial dysfunction and oxidative stress, which subsequently activates pyroptosis through the typical ROS/caspase‐1/GSDMD signaling pathway. Furthermore, MnNi2S3 NE‐mediated EHT enhances the infiltration of CD8+ T lymphocytes into tumors and reverses the immunosuppressive microenvironment. This work demonstrates an electrocatalyst with high HER activity for synergistic gas‐immunotherapy, which may spark electrocatalyst‐based tumor therapy strategies.