The purpose of this study was to assess the effect of leadership styles under the Full Range Leadership Model (transformational, transactional and laissez-faire leadership styles) on employee performance in the case of the Bank of Abyssinia. Furthermore, it was conducted to examine whether employee engagement mediates the influence of Leadership Style on Employee Performance. A quantitative research approach was adopted and a proportional stratified sampling technique was undertaken to determine the sample size, 255. A structured questionnaire was administered in East Addis Ababa District of BOA. Descriptive statistics and inferential statistics were computed using Statistical Package for social sciences (SPSS) version 22. The correlation analysis revealed that both transformational and transactional leadership styles have a significant positive association with employee engagement and employee performance. However, laissez-faire had a non-significant relationship with employee engagement and a significant negative association with performance. The multiple regression of employee performance on each leadership style and employee engagement revealed that transformational leadership and employee engagement has a significant positive effect while laissez-faire has a significant negative effect on performance. Transactional leadership, on the other hand, was revealed to be a non-significant predictor of performance. Mediation analysis was also performed, which revealed the existence of a partial mediation effect only for transformational leadership. The importance of training supervisors and developing a tailored employment engagement strategy were emphasized