Employee well-being has become a more prominent subject of discussion over the past two decades and has been proposed as a vital component of social sustainability within the workplace [1,2]. Broadly speaking, social sustainability within the organizational context can be conceptualized as the social dimension involving both employees and society, which is shaped by and, reciprocally, shapes business practices, thereby influencing the future conditions and environment of the organization [3,4]. From the employees’ perspective, prioritizing their well-being contributes to sustained health and happiness in their jobs, ultimately leading to enhanced performance outcomes [5]. More specifically, a sustainable workforce effectively mitigates the costs associated with burnout, absenteeism, and personnel turnover [6]. Caring for employees’ well-being is thus equally as important as focusing solely on performance outcomes. Considering that high levels of well-being yield performance improvements and vice versa, many scholars have emphasized the need to create a ‘sustainable well-being-productivity synergy’ (e.g., [2]). This synergy implies that investing in employee well-being also benefits the organization in terms of increased work performance and that both aspects are mutually reinforcing. As such, a positive feedback loop is created that can be maintained over the long term.

Given the pivotal role that organizational behavior plays in shaping employee experiences, the achievement of this synergy is contingent upon the leaders within the organization. Traditionally, scholars have conceived of leadership as a hierarchical influence process originating from a single individual within work teams—the formal leader [7] (e.g., a manager). However, a contemporary trend is emerging where team members are assuming additional responsibilities and engaging in tasks conventionally attributed to formal leaders (e.g., [8]). This phenomenon is termed shared leadership, which implies that the primary source of influence within a team not only derives from the formal leader but also from team members. As a result, leadership can be assumed by both formal leaders, who hold officially recognized hierarchical positions above a team, as well as by leaders within the team (i.e., peer leaders) acting from the position of a team member. Specifically, the conceptual framework of shared leadership, as articulated by Pearce and Conger [9] (p. 1), encapsulates “a dynamic, interactive influence process among individuals in groups for which the objective is to lead one another to the achievement of group or organizational goals or both”.

Nonetheless, the efficacy of shared leadership may hinge on the content of the leadership being shared. To attain a sustainable well-being-productivity synergy and promote enduring well-being within the workplace, it is crucial to understand how organizational behavior is related to different desired outcomes. A considerable body of research has examined the organizational behavior of formal leaders in agile or self-managing teams (e.g., [10,11]). However, less is known about the specific behaviors exhibited by peer leaders in shared leadership contexts and their contributions to desired work outcomes. Moreover, it remains unclear whether these contributions vary across different team characteristics. This knowledge gap may result in suboptimal implementations of shared leadership in practice, consuming the time and effort of both the formal leader and the team, with potentially negative consequences for the team and the organization as a whole.

Edelmann et al. [12] initiated the identification of various leadership behaviors of peer leaders. Through an extensive qualitative study encompassing interviews and expert panels, the researchers developed a peer leadership taxonomy that comprises 10 peer leadership roles and 37 functions (i.e., specific behaviors associated with each role). In the practical implementation of shared leadership, employing such a comprehensive set of roles establishes a framework that aids team members in navigating diverse behaviors. However, it remains unclear which of these identified roles and functions play a crucial role in contributing to distinct work outcomes.

Recent empirical studies and meta-analytic reviews have consistently unveiled positive associations between shared leadership structures and critical organizational outcomes. These outcomes encompass a spectrum of dimensions, including team performance and team effectiveness (e.g., [7,13]), as well as individual performance indicators like organizational citizenship behaviors (OCBs) (e.g., [14]). Furthermore, researchers have adeptly demonstrated links between shared leadership and employees’ well-being (e.g., satisfaction with one’s job or team) (e.g., [13,15]), along with team cohesion (e.g., [16]). Notably, research has demonstrated that shared leadership goes beyond the traditional realm of vertical leadership, making a significant contribution to team performance and overall effectiveness [17]. Given that shared leadership can also make a substantial contribution to overall employee well-being, it is argued that this leadership approach concurrently advances social sustainability within the workplace [18]. For instance, according to Pearce and Akanno [19], adopting a shared leadership structure is likely to yield a more resilient management system that is better equipped to facilitate organizational sustainability.

Interestingly, existing research has presented instances of null effects or even inverse correlations between shared leadership and team performance (e.g., [20,21]). Within the context of shared leadership theorization, it is necessary to elucidate these discrepancies. One plausible explanation for these divergent findings resides in the multifaceted ways by which shared leadership can be implemented, thereby influencing the resulting outcomes. Specifically, shared leadership entails team members assuming distinct roles and shouldering corresponding responsibilities within these roles. These roles align with established conceptions of effective teams in which specific roles and associated accountability are argued to be important elements for optimal team functioning (e.g., [22]). In delving deeper into these roles, the efficacy of shared leadership appears to be intrinsically linked to the content of these designated roles.

Over the past fifty years, much of the leadership research has aimed to identify the leader behaviors contributing to team performance, resulting in a plethora of studies with substantial variations in the number and types of behaviors investigated. Yukl et al. [23] noted that many of these studies concentrated on one or two broadly defined behavioral categories, with only a few delving into multiple specific leader behaviors, leading to an incomplete understanding of the diverse ways leaders contribute to team success [24]. Furthermore, Yukl et al. [23] observed that most analyses relied solely on the aggregate of the broadly defined behavioral categories without considering their underlying functions, which challenges the interpretation of leader behavior effectiveness. Thus, to advance the leadership effectiveness research, Yukl et al. [23] underscore the importance of examining the influence of the individual underlying behaviors, especially when they differ in their relevance for achieving an outcome.

Recognizing the conceptual ambiguity in the literature, numerous efforts have been made to develop more precise leadership taxonomies. For instance, a recent exploratory study by Petermann and Zacher [10] sought to inductively construct a behavioral taxonomy related to workforce agility. Nevertheless, organizational research to date has mainly centered on the distinct leadership behaviors expected from formal leaders and their consequences [7], leaving the impact of leadership behaviors fulfilled by peer leaders largely unexplored. As a consequence, researchers and practitioners in the field of shared leadership still encounter challenges in understanding the specific peer leadership behaviors that are important for achieving favorable outcomes [25]. This knowledge deficit may lead to suboptimal implementations of shared leadership in practice, incurring an expenditure of time and effort from both the formal leader and the team. Such implementations might not yield the anticipated positive outcomes and, in some instances, might even result in less desirable outcomes. Consequently, further research is required to delve into the pivotal roles that peer leaders can assume to advance social sustainability.

Addressing the existing ambiguity in the shared leadership literature, our research seeks to comprehensively examine the relationship between diverse leadership behaviors exhibited by peer leaders and sustainable work outcomes. To comprehend the factors contributing to effective team leadership, researchers often adopt a functional approach (e.g., [26]). In this perspective, the leader’s primary responsibility is to address whatever is not adequately managed for the group’s needs [27]. Essentially, this approach focuses on identifying team needs and determining the specific behaviors leaders should exhibit to meet those needs. In this context, the term function denotes any specific behavior aimed at enhancing outcomes. Leaders can be deemed effective to the extent that they ensure the performance of a defined set of leadership functions necessary to meet the team’s needs [28]. Within this framework, leadership functions that share thematic content can be combined into an overarching leadership role that peer leaders can occupy. According to the organizational role theory, a role constitutes the sum of behaviors expected from an individual [29,30]. Consequently, a role encompasses a cluster of content-related functions representing specific behaviors that an individual is expected to fulfill [31]. Working with overarching roles may enhance manageability, particularly for individual team members assuming leadership roles, and role clarity for everyone involved. For example, more specific functions entail a clearer definition of responsibilities, potentially reducing the likelihood of conflicts among peer leaders [32]. These roles should, however, not be used independently of their underlying functions, as these concrete functions provide a structured basis for assigning concrete responsibilities to (peer) leaders.

Over the years, numerous taxonomies have emerged to outline team roles that contribute to effective team performance. However, much of this work has been conducted on ad hoc teams functioning for short durations under low-stress conditions [33]. In addition, according to Driskell et al. [34], there is a considerable divergence in existing team role taxonomies, with recent taxonomies by Mathieu et al. [35] and Driskell et al. [34] incorporating a more varied set of roles. Despite the extensive literature on (formal) leadership and team roles, there is limited knowledge regarding the impact of peer leadership behaviors. Particularly, leadership is a critical element, as in shared leadership, team members are involved in influence processes directed toward collective goals. These roles specifically encompass leadership behaviors by team members. This distinguishes them from regular team roles that are typically related to specific tasks or positions in the team and that do not inherently assume goal-directed influence.

In search of more differentiated leadership behaviors for both formal leaders and peer leaders, Morgeson et al. [24] conducted a review of the existing literature and formulated a framework comprising 15 essential leadership functions. However, one limitation of this framework is that it focuses exclusively on team performance (i.e., what the team needs for goal accomplishment). We posit that functions can yield multiple beneficial outcomes, particularly in promoting social sustainability, wherein the consideration of employee well-being becomes imperative. Another limitation is that Morgeson et al.’s framework lacks differentiation between functions for formal leaders and peer leaders. This abstraction is needed and important, as peer leaders and formal leaders may exhibit different functions with potentially different outcomes.