<p>Plants are susceptible to a wide range of biotic stressors to which they exhibit diverse yet distinct responses. Central to their responses is the modulation of redox status, where the equilibrium between the generation of reactive oxygen species (ROS) and antioxidant defense plays a critical role. Reduced glutathione (GSH), a key redox-active molecule, performs pivotal functions in maintaining cellular redox homeostasis and modulating defense mechanisms during biotic stress. Emerging evidence suggests that GSH, along with its enzymatic counterparts including glutathione peroxidases, glutathione reductase, and glutathione S-transferases, activates plant defense responses by multiple ways such as by (1) triggering the activation of defense-related genes and the production of defense compounds including phytoalexins, (2) preventing excessive cell damage and facilitating controlled cell death during hypersensitive response, (3) influencing salicylic acid and jasmonic acid pathways to shape the systemic acquired resistance and induced systemic resistance, respectively, and (4), conjugating with and detoxifying pathogen-secreted toxins and other harmful compounds produced during pathogen attack, thereby protecting plant cells from potential damage. Additionally, recent studies have also highlighted the key role of GSH in the modulation of ferroptosis, an iron-dependent controlled cell death. Therefore, GSH can be used to manipulate the plant responses to invading pathogens. However, a comprehensive understanding of the intricate interplay among redox dynamics, ROS signaling, and the pivotal role of GSH during biotic stress is essential for devising effective strategies to bolster plant resilience and optimize agricultural productivity under biotic stress. This review synthesizes current research insights into redox biology and highlights the importance of GSH in plant biotic stress responses.</p>