Transthoracic echocardiography (TTE) and Cardiac Magnetic Resonance (CMR) have complementary roles in the severity grading of mitral regurgitation (MR). Our objective was to systematically review the correlation of MR severity as assessed by TTE and CMR. We searched MEDLINE and Cochrane Library for original series published between January 1st, 2000 and March 23rd, 2020. We used Cohen’s kappa coefficient to measure agreement between modalities. We plotted a hierarchical summary receiver operator characteristic (HSROC) curve and estimated the area under the curve (AUC) to assess the concordance between the two imaging modalities for the detection of severe MR. We identified 858 studies, of which 65 underwent full-text assessment and 8 were included in the meta-analysis. A total of 718 patients were included (425 males, 59%) in the final analysis. There was significant heterogeneity in the methods used and considerable variation in kappa coefficient, ranging from 0.10 to 0.48. Seven out of eight studies provided the necessary data to plot HSROC curves and calculate the AUC. The AUC for detecting severe MR was 0.83 (95% CI 0.80 to 0.86), whereas the AUC for detecting moderate to severe MR was 0.83 (95% CI 0.79 to 0.86). The agreement between TTE and CMR in MR severity evaluation is modest across the entire spectrum of severity grading. However, when focusing on patients with at least moderate MR the concordance between TTE and CMR is very good. Further prospective studies comparing hard clinical endpoints based on the CMR and TTE assessment of MR severity are needed.