Across species, cooperative behaviour is often organized by distinct social roles such as leaders and followers1, yet the neural mechanisms that support these emergent role dynamics remain unclear. Here we introduce a mouse paradigm that captures leader–follower dynamics during cooperation. In this paradigm, stable social roles emerge through reciprocal interaction and predict learning speed. Disrupting the activity of the medial prefrontal cortex (mPFC), particularly in followers, impairs cooperation and induces complementary shifts in how animals weigh self- and partner-related cues during decision-making. Calcium imaging reveals that the mPFC represents leader–follower dynamics and computes an egocentric social value map of the partner’s position in a role-dependent manner. By integrating these empirical findings with a multi-agent inverse reinforcement learning framework, we identify latent value functions that guide cooperative decisions and are decodable from mPFC activity. These findings identify prefrontal representations of leader–follower dynamics and partner information, revealing how social roles structure asymmetric yet reciprocal influence over joint decisions.