The presence of social groups in pedestrian crowds can have a substantial effect on the overall evacuation process. However, crowds are mostly simplified as a collection of individuals, and the influence of grouping has not been widely considered in pedestrian crowd simulations. In this study, a novel model that accounts for social groups was implemented based on a social force framework to investigate evacuation dynamics in pedestrian crowds. The associated model parameters were calibrated via two group experiments to provide more credible and realistic simulation results. The effects of certain variables (e.g., group size, desired speed, exit width) on the overall evacuation performance and local group behaviour were investigated. The simulation results indicate that group effects facilitated overall crowd evacuation, especially when the exit was wide. The total evacuation time of a pedestrian crowd was shorter when the groups within the crowd were larger. The time intervals for groups of various sizes did not show a significant difference. The group shape was approximated as a rectangle, and the group features were therefore quantified by shape-related parameters (e.g., aspect ratio and area). The rectangle was shown to orient itself along the moving direction. An elongated configuration of the group became increasingly notable when the leader–follower relationship intensified, resulting in a queue-like formation that facilitated the overall evacuation. A certain trend was found that showed an increase in the aspect ratio and a decrease in the normalised area over time. The larger-sized group often seemed to have a smaller aspect ratio but required more space per person during movement. This study deepens the understanding of crowd evacuation dynamics featuring social groups.