Smoke-free policies effectively reduce secondhand smoke (SHS) exposure among non-smokers, and reduce consumption, encourage quit attempts, and minimize relapse to smoking among smokers. Such policies are uncommon in permanent supportive housing (PSH) for formerly homeless individuals. In this study, we collaborated with a PSH provider in San Diego, California to assess a smoke-free policy that restricted indoor smoking. Between August and November 2015, residents completed a pre-policy questionnaire on attitudes toward smoke-free policies and exposure to secondhand smoke, and then 7–9 months after policy implementation residents were re-surveyed. At follow-up, there was a 59.7% reduction in indoor smoking. The proportion of residents who identified as current smokers reduced by 13% (95% CI: −38, 10.2). The proportion of residents who reported never smelling SHS indoors (apartment 24.2%, 95% CI: 4.2, 44.1; shared areas 17.2%, 95% CI: 1.7, 32.7); in outdoor areas next to the living unit (porches or patio 56.7%, 95% CI: 40.7, 72.8); and in other outdoor areas (parking lot 28.6%, 95% CI: 8.3, 48.9) was lower post-policy compared with pre-policy. Overall, resident support increased by 18.7%; however, the greatest increase in support occurred among current smokers (from 14.8 to 37.5%). Fewer current smokers reported that the policy would enable cessation at post-policy compared to pre-policy. Our findings demonstrate the feasibility of implementing smoke-free policies in PSH for formerly homeless adults. However, policy alone appears insufficient to trigger change in smoking behavior, highlighting the need for additional cessation resources to facilitate quitting.