In summary, we identified a specific mechanism, knowledge, by which HIV testing may affect HIV-related stigma. Our results provide evidence suggesting that HIV testing history can influence knowledge and, in turn, reduce stigma. Although we were limited in our analyses regarding the differences in knowledge and stigma depending on the type of HIV test, theory suggests that individuals who receive individualized pre-test counseling will have stronger knowledge gains. Thus, future research should focus on investigating the longitudinal effects of HIV testing engagement on knowledge and stigma, while taking into consideration the type of HIV test the participant gets (i.e., includes a counseling component or simply a biomedical test). In addition, researchers should explore methods to develop effective, resource efficient intervention strategies to increase knowledge and decrease stigma to increase HIV testing service engagement in at-risk populations and improve treatment adherence among PLWH.