Background Childhood chronic physical illness is associated with a greater vulnerability for emotional problems (i.e. depression and anxiety) in childhood. However, little is known about life‐long effects of childhood chronic physical illness on mental health. The present study aims to systematically review evidence for associations between eight chronic physical illnesses with childhood onset (arthritis, asthma, cancer, chronic renal failure, congenital heart disease, cystic fibrosis, type 1 diabetes, and epilepsy) and adult emotional problems. Methods A database search of MEDLINE, PsycARTICLES, PsycINFO, and ScienceDirect was undertaken, and random effects meta‐analyses were used to synthesise evidence from eligible studies. Results In total, 37 studies were eligible for the systematic review (n = 45,733) and of these, 34 studies were included in the meta‐analyses (n = 45,358). There were overall associations between childhood chronic physical illness and adult depression (OR = 1.31; 95% CI [1.12, 1.54]) and anxiety (OR = 1.47; 95% CI [1.13, 1.92]). Separate meta‐analyses for childhood asthma, type 1 diabetes and cancer were also conducted, with cancer being significantly associated with adult depression (OR = 1.19; 95% CI [1.00, 1.42]). Conclusions The effects of childhood chronic physical illness on the risk of emotional problems persist beyond childhood and adolescence. Mental health prevention and intervention strategies targeting children with chronic physical illnesses can have long‐term benefits.