This Royal Irish Academy white paper, ‘Better together: Knowledge co-production for a sustainable society’, provides an overview of knowledge co-production for sustainability and environmental research in Ireland; highlights the benefits and challenges of co-production approaches; and identifies key levers for building capacity and capability for knowledge co-production. Research approaches involving co-production are often suggested as an appropriate means to meet the requirements posed by real-world problems. These approaches bring actors from outside academia into the research process in order to integrate the best available knowledge, reconcile values and preferences, as well as creating ownership of solution option. Embedding co-production approaches within Ireland's research ecosystem in the coming decade will increase our capacity and capability to produce more impactful and usable knowledge to enable our ambitions to create a zero-carbon and resource-efficient economy, and catalyse the necessary transition to a sustainable society. This paper draws on almost 50 case studies of co-production research for sustainability, along with the outputs from the online Royal Irish Academy symposium and workshop ‘Better together: Knowledge co-production for a sustainable society’, which took place on 3 June 2021.