Despite the fact that activities and rituals that require participants to coordinate their actions and move in synchrony – most prominently shown in music and dance – occur universally in human societies and have deep ontological roots, the evolutionary background of this drive to synchronize is still poorly understood. One theory suggests that synchronous movements were used to display group cohesion in early human groups and that interpersonal synchrony is an “honest signal” (i.e., an involuntary, accurate cue) of cooperative ability. While several studies in recent years demonstrated that synchronous actions increased cooperation in later tasks, the aim of the current experiment was to investigate whether an initial cooperative interaction also led to more behavioural synchrony in a later unrelated task. We asked randomly paired, same-gender dyads to solve a jigsaw puzzle either together or each person by themselves. Subsequently, the dyads were instructed to jump at their preferred speed on two separate trampolines positioned opposite each other, while focusing on a mark at the wall behind the other person. We found that dyads that had cooperated on the jigsaw puzzle task synchronized their jumping frequencies significantly more than those individuals that had worked on the jigsaw puzzle by themselves. The effect was evident in both male and female dyads. These results demonstrate that cooperation leads to more involuntary synchronization within a dyad, highlighting the intricate link between synchronized body movements and cooperation in humans.