This study examines the role of leadership capabilities in determining the post-acceleration performance of early-stage technology startups, which are important drivers of job creation and innovation in the economy. Analyzing data from 423 technology-focused startups that participated in Google for Startups accelerators, the research evaluates leadership effectiveness based on feedback from 7,371 co-founders, employees, investors, and advisors. The findings reveal that startups led by highly effective leaders, as assessed through a validated 33-item multi-rater feedback scale, achieve significantly higher revenue, innovation, funding, and operational longevity post-acceleration. Leadership behaviors such as maintaining composure under stress, understanding team aspirations, and fostering teamwork are identified as key predictors of leadership effectiveness ratings. Conversely, behaviors commonly promoted in the startup ecosystem, such as rapid innovation and frequent pivoting, are associated with lower leadership effectiveness ratings. These results underscore the importance of developing strong leadership within technology startups to enhance their potential for growth, job creation, and innovation, offering valuable insights for accelerators, investors, and founders aiming to foster long-term startup growth and scaling.