Systemic inequalities in higher education have contributed to lower retention and completion rates among low-income, first generation, and racially/ethnically minoritized students, who we refer to as "at-promise" students. In response, educators have implemented comprehensive college transition programs that offer students holistic support including academic, social, financial, and major and career support. Scholarship exploring the efficacy of comprehensive college transition programs commonly focuses on the role of this support in promoting academic self-efficacy, retention, sense of belonging, and other intermediate outcomes linked to at-promise college student success. One sorely understudied intermediate outcome related to at-promise college students' success is their confidence in a major and career path (i.e., major and career self-efficacy). This article focuses on a large scale, longitudinal (2015-2020) study of a comprehensive college transition program called Thompson Scholars that offers major and career support to promote at-promise college students' major and career self-efficacy. Based on the Thompson Scholars' approach, we identified a new model for developing major and career self-efficacy among at-promise students called the "At-Promise College Student Major and Career-Self Efficacy Ecology Model" that explains how and why Thompson Scholars promotes students' confidence in their major and career path. This new approach illustrates how educators can curate a developmentally appropriate set of major and career experiences across multiple contexts responsive to at-promise students' multiple assets to build their confidence.