PurposeThis study uses social exchange theory to describe, explain and propose the influence of dyad partners' leadership position structure, which includes the roles they play and their existing and prospective common experience, on their commitment to their dyad and their cooperation.Design/methodology/approachThe study uses the case of equally empowered co-CEOs in a family business, who play the roles of family member, owner and executive; co-CEOs in a startup firm, who play the roles of owner and executive; and co-CEOs in a merger and acquisition (M&A), who play the role of executive. Co-CEOs in family businesses benefit from longer existing and longer prospective dyad longevity than co-CEOs in startups, who, in turn, benefit from longer existing and longer prospective dyad longevity than co-CEOs in M&As.FindingsThe study proposes that the roles the partners play in the dyads, and the existing and prospective longevity of their relationship, positively influence the partners' commitment to the dyad and their level of cooperation.Originality/valueThe study offers a model that has the potential to direct scholars at the formulation of the theory of top management symmetric formal power dyads dynamics and assist family business owners, startup partners, board of directors and co-CEOs in formulating and implementing upper echelons leadership plans to enhance cooperation and coordination between equal partners.