This paper is based on an empirical study using in-depth qualitative interviews that examines how Roman Catholic undergraduate seminarians in the United States understand gender, sexuality and masculinity. The findings describe how seminarians reject interactionist and social constructionist models of gender, and rely on a strict biological based model where sex/gender are seen as a unified concept. This leads them to adopt an “essential male inclusivity”, where they argue that all people assigned male at birth have equal claim to “manhood”, which eases pressures on them to act in gender normative ways. The social-psychological and identity-based motivations of these beliefs are examined in connection to their life in the seminary and other anticipated occupational characteristics. In contrast, the seminary’s mandates around both celibacy and compulsory heterosexuality, make sexuality more fraught than gender for seminarians. The larger consequences of these perspectives are also explored in regard to gender inequality, homophobia, and the lack of acceptance for the LGBTIQ+ community.