<p>Protocatechuic acid (PCA) is a botanical phenolic acid which has received significant interest due to its wide array of pharmacological properties. From 2000 until 2025, this review provides a thorough insight into the progressive pharmaceutical uses of PCA across a wide range of effects. Data show that antioxidant activity is the most widely investigated activity of PCA, mediated by direct free radical scavenging, metal chelation, and regulation of redox-sensitive signal transduction systems. Closely connected to it, PCA has strong anti-inflammatory properties, which suppress pro-inflammatory mediators and cytokines by regulating the activity of significant molecular pathways. In addition to these fundamental processes, PCA has strong organ-protective action in various systems. PCA exhibits neuroprotective activity by reducing oxidative stress, preventing neuroinflammation, controlling apoptosis, preventing protein aggregation, and sustaining neurotransmitter balance and mitochondrial activity. PCA offers cardioprotection through anti-apoptotic, antioxidant, lipid-regulating, and vasodilatory activities, which lead to enhanced endothelial activity and decreased atherosclerotic processes. It demonstrates hepatoprotective, nephroprotective, antimicrobial, anticancer, antidiabetic, and other bioactivities that are frequently linked and act in common through pathways that involve oxidative stress alleviation and inflammatory regulation. This review reveals that the various pharmacological activities of PCA do not act in a separated manner but constitute a network of biological functions with antioxidant and anti-inflammatory functions acting as a focal point leading to downstream therapeutic effects. Accordingly, PCA turns out to be a versatile and multifaceted bioactive agent with high therapeutic potential. Thus, more clinical trials and translational studies are needed to harness its full biomedical potential.</p>