In this paper, an approach to systematically include sustainability into the Technology Readiness Levels (TRL) is proposed. The aim is to answer the question "how can sustainability provide systematic guidance in technology development and early product development?". Results from a case study illustrate that the suggested approach can support i) the inclusion of sustainability into the early design stages, when only limited data and information is available; ii) the enhancement of the comprehensiveness of sustainability and ease of use in the day-to-day engineering working environment; and iii) simplified sustainability assessments without being too simplistic and/or reducing the sustainability scope. The proposed approach is being co-developed in collaboration with a case company, and tests on an actual technology development project are planned. The next steps are related to the application of the proposed approach in other companies to test its robustness and enhance its generalization for application in diverse contexts.