Drawing on self-determination theory, this study proposed a theoretical model to describe how servant leadership influences subordinates’ task performance and helping behavior through the serial mediations of subordinates’ satisfaction of basic psychological needs (including autonomy, competence, and relatedness) and autonomous work motivations (including intrinsic motivation and prosocial motivation) in firefighter teams. We used survey method to collect supervisor-subordinate paired data. Our research participants were 77 team leaders and 213 frontline firefighters working in a city fire department of the Northern Taiwan. Results of multilevel data analysis revealed that: (1) servant leadership satisfied subordinates’ competence need and increased their intrinsic motivation, which advanced subordinates’ task performance; (2) servant leadership satisfied subordinates’ competence and relatedness needs and increased their prosocial motivation, which promoted subordinates’ helping behavior. On the basis of these results, the current study proposed relevant theoretical and practical implications, and provided future research directions.