Digital technologies are profoundly influencing all economic sectors and have potential to contribute towards a sustainable society. At the same time, the production, use and waste management of these technologies, which lie at the core of the economic sector of information and communication technology (ICT), are causing environmental impacts. Previous studies have applied life cycle assessment (LCA) methodology and life cycle thinking to assess current and future direct energy use and climate impact of the global ICT sector. These studies frequently arrive at contradictory results regarding future impacts. Calculation approaches applied differ significantly, the consideration of key aspects varies, fast-growing digital technologies are seldom included in future scenarios and uncertainty analyses are typically limited. The aim of this study is to develop guidelines for assessments of the current and future direct energy use and climate impact of the global ICT sector based on LCA methodology and life cycle thinking. The guidelines have been developed based on literature reviews, the authors’ aggregated and broad expertise in this topic and in workshops. Key aspects in influencing the current and future direct energy use and climate impact of the global ICT sector, covering its three subdomains of end-user devices, networks and data centres as well as all life cycle stages, are identified. These include, for example, the number of end-user devices, number of subscriptions and the annual electricity use of networks and data centres. The guidelines address challenges for practitioners and can contribute towards more transparent and coherent future studies.