The clinical relevance of Tai Chi on pain, stiffness, and physical function in adults with knee osteoarthritis (KOA) has not been established. Therefore, the purpose of the current study was to address this gap. Eight randomized controlled trials from a recent meta-analysis representing 407 participants (216 Tai Chi, 191 control) in adults ≥18 years of age with KOA and included the assessment of pain, stiffness, and physical function using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) were assessed. The inverse variance heterogeneity model (IVhet) was first used to pool standardized mean difference effect sizes (ES) for each outcome. Clinical relevance, i.e., number-needed-to treat (NNT) ≤10 and relative risk reduction (RRR) ≥25% was calculated across assumed controlled risks (ACR) ranging from 0.01 to 0.99. Statistically significant improvements were found for pain (ES, -0.75, 95% CI, -0.99, -0.51; Q = 8.9, p = 0.26; I2 = 21%), stiffness (ES, -0.70, 95% CI, -0.95, -0.46; Q = 9.6, p = 0.21; I2 = 27%), and physical function (ES, -0.91, 95% CI, -1.12, -0.70; Q = 7.2, p = 0.40; I2 = 3%). The intersection of results for a NNT ≤10 and RRR ≥25% yielded high evidence and clinically relevant improvements across a wide range of ACR for pain (0.15 to 0.88), stiffness (0.15 to 0.87), and physical function (0.13 to 0.97). These findings suggest that Tai Chi results in statistically significant as well as clinically important improvements in pain, stiffness, and physical function across a wide range of ACR in adults with KOA.