Preventing sexual violence is a public health priority given its high prevalence and negative impact on young people’s well-being. This study aims to qualitatively explore the elements that young adults in Spain perceive as influencing their willingness to intervene as bystanders in situations of sexual violence against women. Between 2019 and 2020, we conducted a qualitative study based on 20 semi-structured interviews and four focus group discussions in Spain within the framework of the European project PositivMasc. A total of 49 young men and women participated. We followed Braun and Clarke’s proposal of reflexive thematic analysis. The results of this study describe five elements that are perceived as influencing the willingness to intervene when a situation of sexual violence is witnessed by a bystander: being in a non-party, everyday context; having trust in socio-community assets; holding beliefs that challenge rape culture; emotional distance from the aggressors; and emotional closeness to the victims. The findings are useful when designing new interventions and strengthening existing ones. They can also help in the design of awareness campaigns, strategies, and policies that empower potential bystanders with tools, knowledge, and social support to speak up and act against sexual violence.