The causes of undernutrition are often linked to inappropriate complementary feeding practices and poor households’ access to water, sanitation and hygiene (WASH), but limited evidence exists on the combined effect of poor WASH and inappropriate complementary feeding practices on stunted child growth. We assessed the independent and joint contribution of inappropriate complementary feeding and poor WASH practices to stunted growth among children aged 6–23 months in the Jirapa Municipality of Ghana. A community-based cross-sectional analytical study design was used with a sample of 301 mothers/caregivers having children aged 6–23 months. The results indicate that in a multivariable logistic regression model that adjusted for confounders, children receiving both unimproved water and inappropriate complementary feeding had a higher and significant odd of becoming stunted (adjusted odds ratio = 33. 92; 95 % confidence interval 3⋅04, 37⋅17; P = 0⋅004) compared to households having both improved water sources and appropriate complementary feeding practices. Except for unimproved drinking water sources, poor sanitation and hygiene, which comprised the use of unimproved household toilet facilities, washing hands without soap and improper disposal of child faeces were not associated with the risks of stunting among children aged 6–23 months. The combined effect of unimproved water and inappropriate complementary feeding on stunting was greater than either unimproved water only or inappropriate complementary feeding only.