L-carnitine plays a fundamental biological role in the metabolism of lipids and may positively affect blood pressure by decreasing insulin resistance, although the latter remains less clear. We aimed to assess the effects of L-carnitine supplementation on systolic (SBP) and diastolic blood pressure (DBP). A search was conducted using databases of EMBASE, PubMed, Scopus, Cochrane Library, and ISI web of Science from inception to February 2019 without limitations in language. A meta-analysis was conducted on a total of ten eligible randomized controlled trials using a random-effects model to estimate the pooled effect sizes of L-carnitine supplementation on SBP and DBP levels. Results were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). L-carnitine supplementation decreased DBP (-1.162 mmHg, 95% CI: -2.020, -0.303, p = 0.008) without changing SBP levels (-0.085 mmHg, 95% CI: -1.455, 1.285, p = 0.903). Results of the subgroup analyses revealed L-carnitine supplementation decreased DBP levels in participants with overweight and obesity (-1.232 mmHg, 95% CI: -2.297, -0.167, p = 0.023) and with doses of <2 g/d (-1.639 mmHg, 95% CI: -3.038, -0.240, p = 0.022). No evidence of publication bias was observed about the effects of L-carnitine supplementation on SBP (p = 0.307) and DBP (p = 0.729), as evidenced by the results of the Egger's test. In conclusion, L-carnitine supplementation decreased DBP without affecting SBP levels. Research is required to determine the molecular mechanism underlying the relationship between of L-carnitine on blood pressure.