This paper conceptualises the integration of sustainable development principles into foreign language education for specific purposes through the methodological lens of the five core sustainability competencies. Education for sustainable development is approached as a transformative pedagogical paradigm that fosters critical thinking, system awareness, anticipatory competence, ethical responsibility, and collaborative problem-solving, thereby shaping students’ long-term professional identities and decision-making capacities. In this perspective, foreign language education is not limited to linguistic proficiency but becomes a medium for cultivating sustainability-oriented knowledge, values, and skills relevant to contemporary global challenges. This study is grounded in an educational action research framework focusing on foreign language course and curriculum development in higher education. It offers a systematic justification of course structure, intended learning outcomes aligned with sustainability objectives, instructional strategies, and pedagogical interventions designed to promote active and reflective learning. Empirical data are collected from students at Vilnius University and Mykolas Romeris University (Lithuania), complemented by expert insights from environmental law specialists. The findings suggest that embedding sustainable development into Business English curricula enhances students’ professional preparedness, global awareness, and employability in increasingly sustainability-driven labour markets. Students highlighted the value of integrative, collaborative, experiential, and practice-oriented approaches, while experts identified both strategic benefits and methodological limitations. To sum up, this study underscores the strategic importance of integrating sustainability competencies into foreign language education for specific purposes within higher education.