Developing countries are facing sever productivity problems in their construction sectors. Lean Construction has proven to be an effective solution for such situations. However, when it comes to lean implementation, the operational attributes of the countries can cause significant impacts on the priorities, tools and techniques. This paper took Iranian construction as a sample and sought to identify and prioritise the factors that could significantly contribute to the success of the lean implementation in its context. A comprehensive literature review identified 44 critical success factors (CSFs) in a global setting. The factors were classified into four groups and were presented to industry and/ or academic professionals in the form of semi-structured open-ended interviews that enabled collecting experts’ opinion about the priorities to be given. A thematic analysis of the results indicated that lack of awareness and knowledge of lean construction is the main obstacle for the Implementation. It was also established that more priority should be given to Organisational and Project Management Factors when creating Lean Construction implementation roadmap of the country. This is the first study of its type in Iran and is expected to shed light on the factors that can turn the implementation of Lean Construction a successful story, even in this unfavourable context.