Objectives: As advancing evidence on modifiable resources to support mental health in persons experiencing physical disabilities is of particular importance, we investigate whether structural and functional social relationships relate to mental health in people with spinal cord injury (SCI). Methods: Data from 12,330 participants of the International SCI community survey (InSCI) from 22 countries were analyzed. Structural (partnership status, living situation) and functional aspects of social relationships (belongingness, relationship satisfaction, problems with social interactions) were regressed on the SF-36 mental health index (MHI-5), stratified by countries and for the total sample using multilevel models. Results: Functional aspects of social relationships were consistently related to clinically relevant higher MHI-5 scores and lower risk of mental health disorders (MHI-5 >56). Structural social relationships were inconsistently associated with mental health in our sample. Conclusion: This study provides evidence that functional aspects of social relationships are important resources for mental health. Interventions to establish and maintain high quality relationships should be considered in public health interventions and rehabilitation programs to reduce long-term mental health problems in persons experiencing physical disabilities.