To achieve universal health coverage, the scale-up of high impact public health interventions is essential. However, scale-up is challenging and often not successful. Therefore, a systematic review was conducted to provide insights into the factors influencing the scale-up of public health interventions in low- and middle-income countries (LMICs). Two databases were searched for studies with a qualitative research component. The GRADE-CERQual approach was applied to assess the confidence in the evidence for each key review finding. A multi-level perspective on transition was applied to ensure a focus on vertical scale-up for sustainability. According to this theory, changes in the way of organizing (structure), doing (practice) and thinking (culture) need to take place to ensure the scale-up of an intervention. Among the most prominent factors influencing scale-up through changes in structure was the availability of financial, human and material resources. Inadequate supply chains were often barriers to scale-up. Advocacy activities positively influenced scale-up, and changes in the policy environment hindered or facilitated scale-up. The most outstanding factors influencing scale-up through changes in practice were the availability of a strategic plan for scale-up and the way in which training and supervision was conducted. Furthermore, collaborations such as community participation and partnerships facilitated scale-up, as well as the availability of research and monitoring and evaluation data. Factors influencing scale-up through a change in culture were less prominent in the literature. While some studies articulated the acceptability of the intervention in a given sociocultural environment, more emphasis was placed on the importance of stakeholders feeling a need for a specific intervention to facilitate its scale-up. All identified factors should be taken into account when scaling up public health interventions in LMICs. The different factors are strongly interlinked, and most of them are related to one crucial first step: the development of a scale-up strategy before scaling up.