‘Sustainable palm oil’ aims to eliminate deforestation, greenhouse gas emissions, land conflicts and labour abuses from palm oil global value chains while maintaining palm oil production as a vehicle for development in tropical countries. However, smallholder palm oil growers are a small minority of those who are certified as sustainable and persistently face multiple socio-economic challenges. We analysed 100 journal articles that address smallholders, oil palm and issues related to sustainability in order to critically examine the current state of evidence for sustainability upgrading in smallholder palm oil global value chains. We identify a focus on sustainability certification in the academic research agenda that has left key implementation and knowledge gaps on meeting smallholders’ needs outside of a certification framework. An implication of this is that buyers, policy-makers, and consumers do not recognise both the challenges and advantages of small-scale agriculture for sustainable palm oil. We found that certification standards struggle to resolve persistent smallholder challenges, such as low incomes, low yields and insecure land tenure. Certification appears to be a flawed method to conceptualize and measure the sustainability of smallholders. We, therefore, advocate broadening approaches to studying sustainability and smallholder palm oil production, particularly to target issues that are of immediate concern for smallholder farmers as opposed to prioritising productivity. Future research should take inspiration from diverse established fields of research in defining sustainable practices, such as agroecology or agroforestry.