Emerging technologies are increasingly promoted on the promise of tackling the grand challenge of sustainability. A range of assessment and governance approaches seek to evaluate these claims, but these tend to be applied disparately and lack widespread operationalisation. They also face specific challenges, such as high levels of uncertainty, when it comes to emerging technologies. Building and reflecting on both theory and practice, this article develops a framework for Constructive Sustainability Assessment (CSA) that enables the application of sustainability assessments to emerging technologies as part of a broader deliberative approach. In order to achieve this, we first discuss and critique current approaches to analytical sustainability assessment followed by deliberative social science governance frameworks. We then develop the conceptual basis of CSA – blending life-cycle thinking with principles of responsible research and innovation. This results in four design-principles – transdisciplinarity, opening-up, exploring uncertainty and anticipation – that can be followed when applying sustainability assessments to emerging technologies. Finally, we discuss the practical implementation of the framework through a three-step process to a) formulate the sustainability assessment in collaboration with stakeholders, b) evaluate potential sustainability implications using methods such as anticipatory life-cycle assessment and c) interpret and explore the results as part of a deliberative process. Through this, CSA facilitates a much-needed transdisciplinary response to enable the governance of emerging technologies towards sustainability. The framework will be of interest to scientists, engineers, and policy-makers working with emerging technologies that have sustainability as an explicit or implicit motivator.