Bias-based bullying focused on sexual orientation or gender identity in schools has significant negative implications for the academic, social, and emotional well-being of students who identify as lesbian, gay, or bisexual, or who are perceived to behave in gender nonconforming ways. Despite empirical support for the influence of bystander behavior can have on school bullying, information about bystander behavior during bias-based bullying remains limited. Using a thematic narrative analysis, this study analyzed high school students' perceptions of bystander behavior in their school. Results suggest bystanders are observed to enact a range of responses that fall into three categories: (a) passive avoidance, (b) victim support, or (c) joining the bullying situation. Furthermore, the motivation of bystanders was described within the themes of (a) fear, (b) individual characteristics, (c) relationships, and (d) personal experience. By drawing from the daily lived experiences of adolescents, the current study offers greater insight into youth perspective on how future strategies could address bias-based bullying in schools. This study is foundational to increase the ecological validity of efforts to quantify bias-based bullying.