Back-channel negotiations are commonplace in peace negotiations and can serve as crucial mechanisms for reaching agreements. While there has been a moderate increase in scholarship examining back-channel negotiations in the last two decades, none has explored the gendered nature of these spaces. This article analyzes how and why back-channel negotiations are highly gendered processes and why their gendered nature matters for sustainable peace. We begin with a review of the current literature on back-channel negotiations and discuss how and why they are critical mechanisms in peace negotiation and agreement processes. Next, we show how women’s inclusion in peace negotiations and agreement practices matters for sustainable peace. Thereafter, we discuss how secret negotiation spaces are infused with gendered power and masculine logics of war and peace. We argue that three key features of back-channel negotiations—secrecy, uncertainty, and limited trust—come together to create an echo chamber of hypermasculinity ideas, values, styles, and norms that prevent women from achieving descriptive and substantive representation inside fundamental secret negotiation spaces. This article adds to the developing literature on back-channel negotiations and helps us better understand how and why women and their interests are regularly excluded from peace processes despite the global prominence of the United Nations’ Women, Peace, and Security agenda.