Objective: Mindfulness-based interventions (MBIs) can reduce risk of depressive relapse for people with a history of recurrent depression who are currently well. However, the cognitive, affective and motivational features of depression and anxiety might render MBIs ineffective for people experiencing current symptoms. This paper presents a meta-analysis of randomised controlled trials (RCTs) of MBIs where participants met diagnostic criteria for a current episode of an anxiety or depressive disorder. Method: Post-intervention between-group Hedges g effect sizes were calculated using a random effects model. Moderator analyses of primary diagnosis, intervention type and control condition were conducted and publication bias was assessed. Results: Twelve studies met inclusion criteria (n = 578). There were significant post-intervention between-group benefits of MBIs relative to control conditions on primary symptom severity (Hedges g = 20.59, 95% CI = 20.12 to 21.06). Effects were demonstrated for depressive symptom severity (Hedges g = 20.73, 95% CI = 20.09 to 21.36), but not for anxiety symptom severity (Hedges g = 20.55, 95% CI = 0.09 to 21.18), for RCTs with an inactive control (Hedges g = 21.03, 95% CI = 20.40 to 21.66), but not where there was an active control (Hedges g = 0.03, 95% CI = 0.54 to 20.48) and effects were found for MBCT (Hedges g = 20.39, 95% CI = 20.15 to 20.63) but not for MBSR (Hedges g = 20.75, 95% CI = 0.31 to 21.81). Conclusions: This is the first meta-analysis of RCTs of MBIs where all studies included only participants who were diagnosed with a current episode of a depressive or anxiety disorder. Effects of MBIs on primary symptom severity were found for people with a current depressive disorder and it is recommended that MBIs might be considered as an intervention for this population.