Objective: Suicide is a major public health concern in the United States, but few effective and scalable interventions exist to help those with suicidal thoughts. We hypothesized that reading first-person narratives about working through suicidal thoughts would reduce the desire to die among adults and that this effect would be mediated by increased perceived shared experience and optimism. Method: Using a randomized waitlist-controlled trial, we tested the effect of digital narrative-based bibliotherapy among 528 adults visiting a social media platform dedicated to providing mental health support. Participants were randomized to either a treatment condition (n = 266), in which they read one suicide narrative per day for 14 days or to a waitlist control condition (n = 262). The primary outcome was a measure of desire to die assessed daily for the 14-day trial period and at 2-week follow-up. Results: Participants in the treatment condition reported lower desire to die than participants in the control condition during the 14-day trial period (β = −0.26, p = .001) and at 2-week follow-up (t = −2.82, p = .005). Increased perceived shared experience (indirect effect b = −0.55, p < .001) and optimism (indirect effect b = −0.85, p < .001) mediated the effect of treatment on desire to die. Conclusions: Digital narrative-based bibliotherapy may be an effective intervention for those at risk for suicide, and may work in part by increasing feelings of perceived shared experience and optimism. Future research is needed to test the generalizability of these results to other platforms, groups, and conditions.