Major Depressive Disorder affects about 350 million people worldwide, and about one-third of the patients are considered treatment-resistant. Furthermore, available antidepressants take usually two weeks for the onset of their antidepressant effect. Recent open label trials show that psychedelics, such as ayahuasca and psilocybin, hold promise as fast-onset antidepressants. Although promising, these studies were not controlled for the placebo effect. To address this issue, and to further test the antidepressant effects of ayahuasca, we conducted a parallel arm, double blind randomised placebo-controlled trial, in patients with treatment-resistant major depression. Thirty-five patients with treatment-resistant major depression received a single dose of ayahuasca or placebo. We measured as primary outcome the change in the Hamilton Depression Rating scale (HAM-D) seven days after the dosing session, and as secondary outcomes the changes in Montgomery-Asberg Depression Rating Scale (MADRS), and response rates at one day (D1), two days (D2) and seven days (D7) after dosing, and remission rates at D7. This study is registered with http://clinicaltrials.gov (NCT02914769). We observed robust evidence of rapid antidepressant effects of a single dosing session with ayahuasca when compared to placebo. HAM-D scores at D7 were significantly lower in patients treated with ayahuasca than in those treated with placebo (p=0.019; Cohen's d=0.98). MADRS scores were significantly reduced in the ayahuasca group compared to the placebo group at all endpoints (at D1 and D2, p=0.04; at D7, p<0.0001). Between-group effect sizes increased from D1 to D7 (D1: Cohen's d=0.84; D2: Cohen's d=0.84; D7: Cohen's d=1.49). Response rates were high for both groups at D1 and D2, and were significantly higher in the ayahuasca group only at D7 (64% vs. 27%; OR = 4.95; p = 0.04; NNT = 2.66). Remission rate was not significantly different between groups. Our study provides new evidence of rapid antidepressant effects of ayahuasca for treatment-resistant major depression.