Background Evidence suggests that top managers’ support influences middle managers’ commitment to innovation implementation. What remains unclear is how top managers’ support influences middle managers’ commitment. Results may be used to improve dismal rates of innovation implementation. Methods We used a mixed-method sequential design. We surveyed (n = 120) and interviewed (n = 16) middle managers implementing an innovation intended to reduce health disparities in 120 US health centers to assess whether top managers’ support influences middle managers’ commitment directly, by allocating implementation policies and practices, or by moderating the influence of implementation policies and practices on middle managers’ commitment. For quantitative analyses, multivariable regression assessed direct and moderated effects; a mediation model assessed mediating effects. We used template analysis to assess qualitative data. Findings We found support for each hypothesized relationship: Results suggest that top managers increase middle managers’ commitment by directly conveying to middle managers that innovation implementation is an organizational priority (β = 0.37, p = 0.09); allocating implementation policies and practices including performance reviews, human resources, training, and funding (bootstrapped estimate for performance reviews = 0.09; 95 percent CI: 0.03, 0.17); and encouraging middle managers to leverage performance reviews and human resources to achieve innovation implementation. Practice Implications Top managers can demonstrate their support by directly conveying to middle managers that an initiative is an organizational priority, allocating implementation policies and practices such as human resources and funding to facilitate innovation implementation, and convincing middle managers that innovation implementation is possible using available implementation policies and practices. Middle managers may maximize the influence of top managers’ support on their commitment by communicating with top managers about what kind of support would be most effective in increasing their commitment to innovation implementation.