Objectives To systematically review and synthesize the effects of soft braces on pain and on self-reported and performance-based physical function in patients with knee osteoarthritis. Data Sources The following electronic databases were searched from inception to April 20, 2016: The Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, EMBASE, CINAHL, SPORTDiscus, Web of Science, and PEDro. Study Selection Randomized controlled trials (RCTs) and nonrandomized controlled trials (non-RCTs), such as controlled clinical trials, crossover studies, and case-control studies, were included. Two reviewers independently screened articles and determined inclusion through predefined criteria. Data Extraction Data related to participant demographics, study design and methods, interventions, and outcomes, including numerical means and SDs, were extracted by 1 reviewer. Methodological quality assessment was independently performed by 2 reviewers. Data Synthesis Eleven studies were identified, including 6 RCTs and 5 non-RCTs. The methodological quality of included RCTs was low. There was a moderate improvement in pain (standardized mean difference [SMD]=.52; 95% confidence interval [CI],.14–.89; P=.007; 284 participants) in favor of wearing a brace compared with not wearing a brace for the immediate, within-group comparison. There was a moderate improvement in pain (SMD=.61; 95% CI,.33–.89; P<.001; 206 participants) and a small to moderate improvement in self-reported physical function (SMD=.39; 95% CI,.11–.67; P=.006; 206 participants) in favor of patients receiving a soft brace versus standard care for the prolonged effect, between-group comparison. Conclusions Currently available evidence indicates that soft braces have moderate effects on pain and small to moderate effects on self-reported physical function in knee osteoarthritis. These findings highlight the importance of soft braces as a technique to improve pain and physical function in both the short- and long-term. Additional high-quality studies are warranted to improve confidence in the findings.