Undocumented migrants face cumulative difficulties like precarious living and working conditions or exclusion from health services that might negatively influence their health. Little is known about the evolution of undocumented migrants’ self-reported health (SRH) and mental health after they get documented. This study aims to observe the effect of legal status regularization on SRH and mental health in a cohort of migrants undergoing regularization in Geneva, Switzerland. We evaluate SRH with the first item of the Short Form Survey (SF12) and depression as a proxy of mental health with the PHQ-9 questionnaire over four years among 387 undocumented and newly documented migrants. Using hybrid linear models, our data show that regularization has no direct effect on SRH, but has direct positive effects on mental health in a longitudinal perspective, even when controlling for competing factors. The arrival of the pandemic did not alter these effects. Migrants tend to evaluate their subjective health status more positively than the prevalence of screened depression shows. Those findings point towards better targeted policies that could reduce the burden of depression among undocumented migrants.