A growing body of evidence suggests positive psychological capital (PsyCap) strongly predicts well-being and performance at work. However, most of this empirical research has used self-report survey designs, increasing the possibility of self-report and mono-method bias. The current study used a multitrait-multimethod (MTMM) research design and condition-based regression analysis to examine the effect of PsyCap on job well-being and work role performance beyond self-report bias. Findings from 416 full-time employees within 208 coworker pairs showed that self-reported and informant-reported PsyCap were predictive of job well-being and work role performance. However, multitrait-multimethod analyses showed monomethod measures may inflate the strength of association between PsyCap and work outcomes. Implications for future applied positive psychology research controlling for self-report and monomethod bias with multiple data sources are discussed.