Purpose: Transformational leadership (TFL) has been suggested to create positive changes in employees with the goal of developing them into leaders. The authors integrate this well-established leadership style with recent research on idiosyncratic deals (i-deals). The authors suggest TFL as a predictor of task and development-based i-deals, and propose i-deals as a mediating mechanism linking TFL to employee outcomes (job satisfaction, job stress and manager-rated performance). Design/methodology/approach: The authors used a time-lagged research design, and collected four waves of data from 140 employees and 78 leaders. Findings: TFL was found to be an important predictor of i-deals. I-deals predicted job satisfaction and job stress; and it mediated the relationship between TFL and these two employee outcomes. Yet, i-deals were not associated with employee performance and did not mediate the relationship. Originality/value: First, it shows that transformational leaders who consider employees' unique skills and support their professional growth are more likely to grant personalized arrangements. Second, drawing from social exchange theory, it illustrates that i-deals may act as a linkage between TFL and employee outcomes. The paper bridges leadership and i-deals literature to identify key leverage points through which leaders can enhance employee satisfaction, well-being and performance. © 2023, Emerald Publishing Limited.