Studies investigating the association between maternal adiposity and risk of pre-eclampsia showed contradictory results. Therefore, we performed a meta-analysis of prospective cohort studies to estimate the effect of maternal adiposity on pre-eclampsia. We reviewed 1,286 abstracts and finally included 29 prospective cohort studies with 1,980,761 participants and 67,075 pre-eclampsia events. We pooled data with a random-effects model, and obtained risk estimates for five predetermined bodyweight groups: low, normal-weight (reference), overweight, obese and severely obese. In the cohort studies that unadjusted for pre-eclampsia risk factors, the pooled unadjusted relative risks (RR) with 95% confidence intervals (95%CI) for pre-eclampsia of overweight, obese and severely obese women were 1.58 (95% CI 1.44–1.72, P < 0.001), 2.68 (95% CI 2.39–3.01, P < 0.001) and 3.12 (95% CI 2.24–4.36, P < 0.001), respectively. In those cohorts that adjusted for pre-eclampsia risk factors, the pooled unadjusted RRs for pre-eclampsia of overweight, obese and severely obese women were 1.70 (95% CI 1.60–1.81, P < 0.001), 2.93 (95% CI 2.58–3.33, P < 0.001) and 4.14 (95% CI 3.61–4.75, P < 0.001), respectively. Sensitivity analysis showed maternal adiposity was associated with increased risk of pre-eclampsia in both nulliparous and multiparas women. In conclusion, overweight or obese pregnant women have a substantially increased risk of pre-eclampsia, and maternal adiposity is an independent risk factor of pre-eclampsia.