Since 2014, Europe allocated €5.5 billion in sustainable watershed management, including Nature-Based Solutions (NBS) of green-blue infrastructure to combat aquatic ecosystem decline and climate change impacts (e.g. flooding, urban heat). Reliable integrated Planning Support Systems (PSS) are needed for strategic NBS implementation, an EU priority. In past decades, many PSS for NBS have emerged. However, standard validation procedures for PSS lack, which limits PSS credibility, uptake and hampers strategic NBS planning. While diverse model performance criteria and corresponding validation procedures have been proposed, no standard approach has been agreed on. My proposal, MOVE-NBS, aims to create such a standard: to build a framework of widely agreed holistic performance criteria and validation procedures for PSS. I have three objectives: 1) systematically enquiring expert preferences for model performance and validation; 2) empirically testing selected procedures; and 3) building a novel evaluation and validation framework for PSS. To advance current state-of-the-art, I propose an innovative approach: 1) Multi-Criteria Decision Analysis (MCDA) with leading PSS and NBS experts from science and practice using online preference elicitation; 2) implementing validation procedures in four test cases of real-world NBS planning projects on three continents, using two PSS developed by myself and project partner; and 3) synthesising findings. Academic impact for PSS and the wider environmental modelling community formally capturing current high-level ideas about model performance and validation into standardised procedures, resulting from wide academic consensus. This will critically improve PSS credibility and comparability. For practice, impacts include improved interpretation and reliability of PSS. These impacts should lead to more strategic siting of NBS, and improved realisation of the multiple benefits of green-blue infrastructure for society.