Gun violence is the most pressing public safety problem in American cities. We report results from a randomized controlled trial (N=2,456) of a community-researcher partnership—the Rapid Employment and Development Initiative (READI Chicago)—which provided 18 months of a supported job alongside cognitive behavioral therapy and other social supports. Algorithmic and human referral methods identified men with strikingly high scope for gun violence reduction: for every 100 people in the control group, there were over 11 shooting and homicide victimizations during the 20-month outcome period. Take-up and retention rates were comparable to programs for people facing far lower mortality risk. There is no statistically significant change in an index combining three measures of serious violence, the study's primary outcome. But one component, shooting and homicide arrests, shows a suggestive decline of 64 percent (p=0.15). Because shootings are so costly, READI generates social savings between $174,000 and $858,000 per participant, implying a benefit-cost ratio between 3.8 and 18.8 to 1. Moreover, participants referred by outreach workers—a pre-specified subgroup—show enormous declines in both arrests and victimizations for shootings and homicides that remain statistically significant even after multiple testing adjustments. These declines are concentrated among outreach referrals with high predicted risk, suggesting that human and algorithmic targeting may work better together.