Strong social ties correspond with better health and well being, but the neural mechanisms linking social contact to health remain speculative. This study extends work on the social regulation of brain activity by supportive handholding in 110 participants (51 female) of diverse racial and socioeconomic origins. In addition to main effects of social regulation by handholding, we assessed the moderating effects of both perceived social support and relationship status (married, cohabiting, dating or platonic friends). Results suggest that, under threat of shock, handholding by familiar relational partners attenuates both subjective distress and activity in a network associated with salience, vigilance and regulatory self-control. Moreover, greater perceived social support corresponded with less brain activity in an extended network associated with similar processes, but only during partner handholding. In contrast, we did not observe any regulatory effects of handholding by strangers, and relationship status did not moderate the regulatory effects of partner handholding. These findings suggest that contact with a familiar relational partner is likely to attenuate subjective distress and a variety of neural responses associated with the presence of threat. This effect is likely enhanced by an individual's expectation of the availability of support from their wider social network.