Maternal adiposity deleteriously affects obstetrical health and has been associated with long-term adverse consequences in offspring. Here we conducted an umbrella review encompassing 194 observational meta-analyses, 10 Mendelian randomization studies and 748 interventional meta-analyses to appraise the published evidence on the associations between maternal adiposity and perinatal and offspring outcomes. Evidence grading suggested that 17 (8.8%) observational meta-analyses were supported by convincing evidence for 12 outcomes: maternal adiposity was associated with an increased risk of caesarean delivery following labour induction, infant mortality, Apgar score <7 at 1 min, antenatal depression, offspring overweight and obesity, early timing of puberty onset in daughters, attention deficit hyperactivity disorder, cerebral palsy, congenital heart disease and spina bifida (OR/RR ranging from 1.14 to 2.31), as well as increased offspring body fat percent and fat mass (SMD 0.31 and 0.35, respectively). Among these outcomes, interventional meta-analyses supported that maternal weight loss interventions significantly reduced the risk of antenatal depression but not low Apgar scores; these interventions also could not reduce offspring fat mass or body fat percent. Evidence from Mendelian randomization studies supported a causal relationship between maternal adiposity and gestational diabetes mellitus, preeclampsia, birth size and offspring adiposity. Our findings highlight that while observational meta-analyses reveal associations between maternal adiposity and various adverse perinatal and offspring outcomes, convincing, unbiased evidence or support from Mendelian randomization studies is limited. Maternal pre-conceptional and prenatal weight loss interventions can reduce some, but not all, of these adverse effects.