Humans and social animals interpret the body language of others to infer intentions and adjust their actions instantaneously. To explore neural representations of conspecific kinematics during goal-directed behavior, we trained pairs of freely moving mice to jointly perform a two-alternative forced-choice task. The mice had to discriminate the location of a visual grating to earn water rewards. Using high-speed videography, we showed that mice engage in stereotypical trajectories from the trial initiation site to the chosen reward lick port across hundreds of trials. By decomposing movement into translation and rotation, we were able to reliably predict mouse choices based on head direction changes after stimulus onset. Neuropixels recordings and microendoscopic calcium imaging from frontal cortical areas during task execution revealed single-neuron activity that coincided with or preceded choice-predictive head rotations. When we asymmetrically varied the grating contrast for each mouse on each trial, we observed a leader-follower dynamic with mice presented with lower-contrast gratings more likely to follow their conspecific. In a subset of choice-predictive neurons, the activity patterns differed depending on whether the mouse took the lead or followed its conspecific. We finally built a behavioral model that summarized conspecific movements along a single kinematic axis and could accurately predict mouse choices in follower trials. This confirmed the significant impact of conspecific postural cues on the decision-making process. Our findings suggest that mice actively monitor others to guide their actions, and that task demands may result in a simplified representation of social kinematics within the frontal cortical areas.