The present research is embedded in the professional development and research line, and in the needs of secondary education and first-year university teachers. Evidencing the importance of teachers’ professional training to include specific adaptations and skills on both the intercultural dialogue and understanding—often called Intercultural Competence—is fundamental because of the direct impact for the sustainable development of human beings, groups, and ecosystems. An extensive investigation of the role played by each of the main competencies linked to the following intercultural dimensions was performed: Professional Identity, Ethics and Axiology, Methodology, and Inclusive Education. The integrated methodology used was a cross-study of data, performed after the obtention of a three-cornered evaluation of results collected in focus groups, interviews, and questionnaires. Findings showed the impact of the intercultural dialogue and understanding in education patterns for the sustainable development of society. Other outputs also underlined the relevance of setting up a new ecology of forms, knowledge, attitudes, and educational meanings, further used to update teachers and students’ training in sustainable ecology and cultural diversity. Progress made in these complementary competencies—Professional Identity, Ethics and Axiology, Methodology—were appraised by teachers participating in the present study; the latter showing an increased interest and demand for the intercultural competence, after increasing their proficiency in the other complementary competencies.