With much research recognizing psychological safety as a pivotal force for organizational success, scholars have identified ways to help organizations establish it. However, it remains less understood why some employees perceive lower psychological safety and how to enhance it for them. In this research, we draw on the dual-continua model of mental health, as well as the broaden-and-build and conservation of resources theories to theorize that by providing effective mental health support, organizations can help employees improve their positive mental health, enabling them to see more people at work as sources of support; perceiving an expansion of their job-related supportive network at work can subsequently lead employees to perceive stronger psychological safety. We first conducted a pre-study to establish the relationships between positive mental health, social network, and psychological safety in a cross-sectional survey of 685 full-time workers. We then conducted an eight-week field experiment at a coffeehouse chain, where individuals with and without mild to moderate mental illnesses work together. Employees were randomly assigned to either receive mental health support through using a clinically tested mental healthcare app or use a placebo app. Results show that using the mental healthcare app led to a significant expansion in employees’ perceived supportive network at work, which significantly enhanced their psychological safety. Our research highlights employees’ positive mental health and organizational support for it as foundational for establishing psychological safety, as well as the role of perceived size of supportive network in facilitating interpersonal risk-taking among people experiencing mental health challenges.