Objective To measure the short‐term effects of the Cancer‐PEPSONE programme (CPP) on the partners' received and perceived social support, psychological distress, and quality of life (QOL), as well as explore the role of received social support as a mediator of the intervention effects. Methods Open single‐center randomized controlled trial, trial number 15982171(ISRCTN). Eligible participants were the partners of cancer patients who were concomitantly caring for minors (the well parents). The sample consisted of 35 participants randomly allocated to receive either intervention (n = 17) or support as usual (n = 18). At the 3‐month follow‐up (approximately 1 month after intervention), 24 continued to participate (intervention n = 13, control n = 11). The intervention group selected supporters to participate in CPP (N = 130). Data were obtained using validated questionnaire. Results The multivariate analysis of covariance revealed significant intervention effects (P = .03, η2p = 0.42), with main effects on received and perceived social support. A mediational analysis suggested that CPP may have indirect effects on QOL through received social support. Conclusions Even though the long‐term effects are yet to be studied, CPP seems to increase social support for the well parents' short term, which in turn may improve their QOL. Given the study's low sample size, further replications in larger samples are required.