This research demonstrates social support from fellow group members as unique trigger of additional effort and performance in groups. Support‐induced effort gains are shown both compared with groups without social support and individual work. Study 1 examined existing beliefs about motivating group work among employees with professional group work experience (n = 130). The results revealed social support as one of the most frequently reported sources of group‐induced effort gains. Study 2 explored self‐reported effort intentions in group training scenarios among athletes (n = 94). Finally, Study 3 examined performance as a manifest indicator of effort in an experimental persistence task among students (n = 88). The results of Study 2 and Study 3 showed significant gains due to social support in both self‐reported effort and manifest performance, respectively. Together, the results demonstrate that receiving social support from fellow group members leads to higher effort in groups at the level of existing beliefs about motivating group work, at the level of effort intentions, and at the level of manifest performance behavior. The observed findings cannot be explained by established sources of motivation gains in groups such as social comparison or social indispensability. Copyright © 2014 John Wiley & Sons, Ltd.