Line managers are often responsible for implementing HR practices in organizations. Why do some line managers implement HR practices as intended while others do not? We draw on the concept of accountability focus to highlight that managers' HR implementation behavior is driven by what they feel accountable for, and we examine how accountability focus is shaped by characteristics of managers' role. We test our theoretical model across two field studies: a three‐wave survey with managers and a study with dyads of managers and employees. When managers experienced more autonomy in their HR role, they felt more accountable for outcomes and were less likely to implement HR practices, but this was mitigated when managers also felt competent in their HR responsibilities. More competent managers felt more accountable for processes and in turn were more likely to implement HR practices, which positively related to employees' discretionary effort. Our findings highlight boundaries to managerial autonomy, and theoretical insights about the motivational mechanisms, which drive HR implementation, with implications for employees. We contribute to theory on managerial accountability by elaborating the nomological net of accountability focus and, by developing a measurement scale through several pilot studies, provide opportunities for further research.