Background: There is a great interest in researching prescriptive methods as entrepreneurs demand guidance for start-up processes. A learn-by-doing methodology called lean start-up methodology has influenced tech entrepreneurs. Further, design thinking is another methodology for developing innovation that has been suggested to benefit in a software context. The uncertain nature requiring rapid innovation for software start-ups has sparked the interest in exploring the combination of the methodologies in an entrepreneurial context to utilize the benefits of both. However, the methodologies have been criticized due to a lack of rigor. It is therefore an opportunity to explore applicability of lean start-up in practice and design thinking in a software context to develop a unique methodology integrating lean start-up and design thinking.Purpose: The purpose of this study is to explore the occurrence of the two innovation driven methods lean start-up and design thinking in successful software start-ups, to develop a theory of an integrated methodology that utilizes the benefits of both. The intent is to provide explicit guidance for both scholars and entrepreneurs. Methodology: An exploratory qualitative method was used with an inductive approach, conducting semi-structured interviews with six founders of successful software companies. Conclusion:  The findings advance the understanding of the lean start-up methodology in practice, by extending the aspect of idea development and clarifying the use of iterating aspects of the business model. The findings update the sequence of design thinking when applied in a software context and extend the iterating aspect, to adapt to the need for rapid development. The theory of suggested integration confirms that the first stages of design thinking initiate the idea process, emphasizing early consideration of desirability, viability, and feasibility, while lean start-up is integrated into the product development process, emphasizing rapid iterating development for validation.