This paper aimed to provide insights into the different mediating mechanisms through which servant leadership (SL) and transformational leadership (TFL) affect followers. We also investigated environmental uncertainty as a moderator of the effects of servant leadership and transformational leadership. Based on the results of two experimental studies and one field study, we concluded that both SL and TFL were related to organizational commitment and work engagement; however, the manner in which they exerted their influence differed. SL worked primarily through follower need satisfaction, whereas TFL worked mainly through perceived leadership effectiveness. The moderating influence of uncertainty was inconsistent across the studies.