Youth from advantaged backgrounds have more social relationships that provide access to resources facilitating their educational success than those from low-income families. Does access to and mobilization of social capital also relate to success among the few low-income youth who "overcome the odds" and persist in higher education? Using nationally representative longitudinal data over a 14-year period, this study shows that although access to social capital in families, schools, and communities is positively related to entry into higher education, most forms of adolescent social capital are not independently associated with degree attainment. However, the mobilization of social capital through certain types of mentorship benefits both the college entry and bachelor’s degree attainment of low-income youth, more so than for their more economically advantaged peers. Findings suggest that developing enduring mentoring relationships and new social resources rooted in the higher education context may be especially important in facilitating degree attainment for young adults from low-income backgrounds.