Significant efforts are being made to reduce greenhouse gas emissions across all sectors of the economy to achieve net-zero carbon emissions by 2050. The expansion of lower carbon energy sources has been reshaping the electricity grid generation mix, influencing the entire supply chain. Operational carbon emissions can potentially reach zero in the building sector through cleaner energy grids and on-site zero carbon energy generation. Consequently, embodied carbon in the building life cycle could potentially become increasingly significant in whole life carbon. The selection of construction materials, efficiency of construction and operation processes, and end-of-life strategies are therefore crucial to minimizing life cycle carbon impacts. However, the broader environmental implications of this energy transition remain uncertain. Although studies have explored future scenarios for buildings, the long time horizons and potential for change make accurate life cycle modelling of buildings challenging. The key challenges in assessing building life-cycle impacts in a decarbonizing economy and the evolving roles of designers and the construction sector in achieving net-zero goals are presented. The study contributes to advancing understanding of how decarbonizing energy systems reshape the life-cycle boundaries and priorities for life cycle design in the built environment. By integrating the dynamics of future energy transition into life cycle assessments, it emphasizes the importance of scenario-based prospective life cycle assessment approaches to address the uncertainties associated with technological evolution and policy-driven transformations. The findings highlight the need for the built environment sector to adopt forward-looking design strategies and flexible assessment tools that can explore these dynamic changes. In doing so, the research provides insights for both practitioners and policymakers on how to align material choices, design practices, and assessment frameworks with the broader decarbonization pathways required to achieve global net-zero goals.