The holistic modelling approach required for the long-term integrated urban energy planning is becoming a big challenge since the complexity of cities, as well as their commitments are increasing rapidly. Many municipalities require technical support during the definition of the direction of their long-term energy transition plans. Innovative modelling approaches and the ex-ante impact assessment are necessary steps of the process since the direction adopted by the city will have many long-lasting implications not only in the energy and climate dimensions but also in their social and economic development. This paper presents the overall methodological and modelling approach and the initial results of the developed Advanced Integrated Urban Planning process that has been validated by its application in the cities of Helsinki, Hamburg and Nantes.