This study investigates the impact of leadership styles and team cohesion on employee engagement and performance within workgroups in Nigerian organisations. Drawing on Bass and Avolio's Full Range Leadership Model and Carron's conceptualisation of team cohesion, a quantitative survey design was employed with a sample of 320 employees drawn from five industry sectors banking, telecommunications, manufacturing, public administration, and fast moving consumer goods (FMCG) across Lagos, Abuja, and Port Harcourt Validated instruments assessed transformational, transactional, and laissez faire leadership behaviours, task and social team cohesion, employee engagement, and supervisor rated performance. Pearson correlation and multiple regression analyses revealed that transformational leadership was the strongest positive predictor of both employee engagement (β = 0.41, p <.001) and performance (β = 0.37, p <.001), while laissez faire leadership exerted significant negative effects on both outcomes. Team cohesion mediated the relationship between transformational leadership and employee outcomes, accounting for 23% of the variance in engagement and 19% in performance beyond direct effects. Transactional leadership demonstrated moderate positive associations, predominantly in manufacturing and public sector contexts. These findings have significant theoretical and practical implications for human resource management, leadership development, and organisational effectiveness in the Nigerian corporate environment and, by extension, for emerging market organisations navigating comparable institutional and cultural dynamics.