Transdiagnostic approaches to cognitive behaviour therapy (TCBT) of anxiety disorders have drawn increasing interest and empirical testing over the past decade. In this paper, we review evidence of the overall efficacy of TCBT for anxiety disorders, as well as TCBT efficacy compared with wait-list, treatment-as-usual, and diagnosis-specific cognitive behaviour therapy (CBT) controls. A total of 11 studies reporting 12 trials (n = 1933) were included in the systematic review. Results from the meta-analysis of 11 trials suggest that TCBT was generally associated with positive outcome; TCBT patients did better than wait-list and treatment-as-usual patients, and treatment gains were maintained through follow-up. The pooled estimate showed a moderate treatment effect, however with large heterogeneity suggesting differences in treatment effects between the studies. Also, all the included trials, apart from one, were judged to be associated with a high risk of bias. Only one study compared TCBT with diagnosis-specific CBT suggesting treatment effect of TCBT to be as strong as diagnosis-specific CBT. This study not only cautiously supports evidence for the efficacy of TCBT, but also suggests the need for more high-quality, large-scaled studies in this area. Transdiagnostic treatments offer great clinical promise as an affordable and pragmatic treatment for anxiety disorders and as a specialized treatment for co-morbid and other-specified anxiety disorders.