Governments worldwide are setting ambitious targets for offshore renewable energy development (ORD). However, deployment is constrained by alack of understanding of the environmental consequences of ORD, with impacts on protected birds forming a key environmental consenting challenge. Assessing the impacts of ORD on marine birds is challenging, utilizing interlinked approaches to understand complex behavioural, energetic, and demographic processes. Consequently, there is considerable uncertainty associated with ORD assessments for marine birds, with current methods failing to quantify uncertainty in a scientifically robust, evidence-based manner. This leads to a high degree of precaution and alack of confidence in the evidence used to inform ORD consenting decisions. We review the methods used to estimate ornithological ORD impacts in the UK, a country at the forefront of ORD. We identify areas in which uncertainty quantification could be improved through statistical modelling, data collection, or adaptation of the assessment process. We develop a framework for end-to-end quantification of uncertainty, integrating uncertainty estimates from individual stages of the assessment process. Finally, we provide research recommendations to better quantify and reduce uncertainty, to lower future ORD consenting risk. These recommendations extend beyond the UK and could improve impact assessments in other countries with different legislative frameworks.