Research on vocational rehabilitation for clients with severe mental illness over the past 2 decades has yielded inconsistent findings regarding client factors statistically related to employment. The present study aimed to elucidate the relationship between baseline client characteristics and competitive employment outcomes-job acquisition and total weeks worked during an 18-month follow-up-in Individual Placement and Support (IPS). Data from 4 recent randomized controlled trials of IPS were aggregated for within-group regression analyses. In the IPS sample (N = 307), work history was the only significant predictor for job acquisition, but receiving Supplemental Security Income-with or without Social Security Disability Insurance-was associated with fewer total weeks worked (2.0%-2.8% of the variance). In the comparison sample (N = 374), clients with a diagnosis of mood disorder or with less severe thought disorder symptoms were more likely to obtain competitive employment. The findings confirm that clients with severe mental illness interested in competitive work best benefit from high-fidelity supported employment regardless of their work history and sociodemographic and clinical background, and highlight the needs for changes in federal policies for disability income support and insurance regulations.