Osteoarthritis (OA) is a prevalent degenerative joint disease predominantly affecting the elderly and is characterized by cartilage degradation, synovitis, and subchondral bone sclerosis. Despite its widespread occurrence, no effective pharmacological interventions currently exist to halt or reverse disease progression. Polyphenolic compounds, a diverse class of plant-derived substances, have attracted considerable attention for their potent anti-inflammatory and antioxidant activities. This review summarizes recent advances in understanding the multifaceted roles of polyphenols in OA. Specifically, polyphenols protect chondrocytes and preserve the extracellular matrix by mitigating oxidative stress, suppressing inflammation, regulating autophagy and cholesterol metabolism, and inhibiting programmed cell death pathways, including apoptosis, pyroptosis, and ferroptosis. Furthermore, they exert protective effects on synovial tissue by regulating macrophage polarization and inhibiting pathogenic fibroblast activation, while also contributing to the maintenance of subchondral bone homeostasis. Recent progress in nanotechnology-based delivery systems, designed to overcome the poor solubility and limited bioavailability of polyphenols, is also highlighted. Collectively, this review integrates mechanistic insights with emerging therapeutic strategies, underscoring the potential of polyphenolic compounds as disease-modifying agents for OA.