<p>Integrated Assessment Models (IAMs) are central to informing climate policy and sustainable development, yet face longstanding criticisms related to transparency, legitimacy, and exclusion of societal actors. This paper argues that a transdisciplinary (TD) approach, offers a promising pathway to address these critiques. However, it can be overwhelming for researchers who know little about TD to grasp the core principles that ground and guide such an approach. We identify and systematise thirteen TD principles that underpin a TD approach from the literature and categorise them as project, process, and outcome principles, in an accessible format. Drawing on the DIAMOND project, which aims to expand and co-produce six IAMs through collaboration with societal actors, we use a qualitative approach to examine how these principles are perceived by modelling teams in a series of workshops. We find that while some principles, such as engaging with scientific and non-scientific actors, are embraced, others, including practicing reflexivity and systemic thinking, require strengthening or more nuanced understandings. We argue that reflecting on a project process through these TD principles and embedding the principles more intentionally can help IAMs better respond to the challenges and criticisms they face. By shifting IAMs toward more open, co-owned, and context-sensitive approaches, TD principles can support IAMs to inform more socially robust and actionable climate solutions. The paper contributes a grounded, accessible framework to advance a TD research approach not only in integrated assessment modelling, but all large-scale projects taking on a TD approach to address complex sustainability challenges.</p>