Grounded in the startup accelerators literature, we evaluate whether the leadership capabilities of founders and C-suite executives as assessed by co-founders, employees, investors, and advisory board members during their time in the accelerator predict startups’ future performance trajectories. Analyzing data on 430 technology-focused startups that participated in the Google for Startups accelerators and their 966 founders and C-suite executives, we find that startups with more effective leaders as evaluated by affiliates achieved higher revenue, innovation, funding, scaling, and longevity post acceleration. We examine leaders’ multi-rater feedback evaluations by their 7,371 affiliates using a validated 33-item scale to understand what behaviors distinguish leaders who achieve superior ratings by affiliates. Our findings underscore the critical importance of leadership capabilities in startups’ future performance trajectories.