Climate change is a human problem, caused by humans, affecting humans, and requiring a human-centric solution. CAMPAIGNers aims to make low-carbon lifestyles a major part of the solution by identifying lifestyle transformation potential, and associated barriers and enablers across 5 continents and 16 major cities with over 20 mil. residents. Feasible pathways to GHG mitigation are developed to include the empirically validated lifestyle changes, and are applied to the principal integrated modelling tools used in the EU to provide robust insights into the system-level impacts of large-scale lifestyle transformation. CAMPAIGNers builds on previous consortium-led projects that substantially improved the understanding of societal structures and interventions that encourage lifestyle shifts, and identified limitations to the existing evidence-base. Namely, current lifestyle transformation research is either limited to narrow, specific contexts or groups, or deals in hypothetical behaviours where most citizens do not have real experiences to draw on. CAMPAIGNers’ ground-breaking approach overcomes these drawbacks by implementing a ‘goal-setting network’, where over 100,000 citizens receive and create challenges to try out tailored adaptations to their daily routines via an engaging app. Their responses to these challenges, associated treatments, and short questionnaires will deliver unprecedented data of behavioural processes, (local) barriers to change, and motivators, allowing for empirically-based scientific support of cities in crafting policies to encourage low-carbon lifestyles. Together with local, national and EU policy makers insights are analysed regarding the ‘right-level-to-act’ and policy-ready recommendations are jointly derived. A workshop in the EU Parliament, hosted by First-Vice President Ms. McGuinness, and supported by 9 more MEPs from 6 countries and 4 political parties, will ensure high-level feedback and contribute to consensus building.