Background: Although women are encouraged to achieve good diet quality in preconception and pregnancy, the benefits on perinatal outcomes have not been established. Objective: To systematically review and quantify the association between diet quality and adverse perinatal outcomes. Search strategy: Medline, Embase, Food Science and Technology Abstracts and CINAHL were searched up to 5th March 2020. Selection criteria: Two authors independently screened, selected and coded relevant prospective cohort studies. Data collection and analysis: Thirty-three studies (315,431 participants) were included in the meta-analysis. Odds ratios and mean differences from individual studies were pooled using random-effects models. Main Results: The pooled results for the association between diet quality and excessive (OR: 0.91; 95 CI: 0.76, 1.10) or inadequate (OR: 0.90; 95 CI: 0.70, 1.17) gestational weight gain were not statistically significant. Women in the top tertile of diet quality scores during prepregnancy or pregnancy had a lower risk of gestational diabetes (OR: 0.77; 95 CI: 0.65, 0.90), hypertensive disorders of pregnancy (OR: 0.87; 95 CI: 0.83, 0.92), preterm birth (OR: 0.77; 95 CI: 0.66, 0.89), small for gestational age (OR: 0.88; 95 CI: 0.79, 0.99) and low birth weight (OR: 0.60; 95 CI: 0.37, 0.99) compared to those in the bottom tertile. No studies were found for delivery mode. Conclusions: Data from prospective cohort studies support the potential of improving maternal diet quality in the effort to prevent adverse perinatal outcomes. Funding: Canadian Institutes of Health Research HLT 151517, National Natural Sciences Foundation of China No. 81661128010 Keywords: Diet quality, perinatal outcomes.