Individuals with mental health needs in the criminal justice system often face stigma, which can exacerbate their challenges, affecting their rehabilitation and reintegration. Research on how this specific group is stigmatized and the intersectional factors that differentiate it remains limited. This research aims to explore social workers’ perceptions of the stigmatization of individuals with mental health needs within the criminal justice system, from an intersectional approach. This qualitative study conducted in-depth interviews with 18 social workers. The data were analyzed using thematic analysis via MAXQDA. Two themes were identified from the analysis: “stigmatization of people with mental health needs involved in the criminal justice system,” and “intersectional differences in stigmatization.” The results indicate that social workers believe that their clients were stigmatized due to their mental health needs before relating to the criminal justice system, and after their involvement with the system, the stigma of being an “offender” became more prominent. The stigmatization of the participants’ clients varies by gender, class, education, ethnicity, and crime type, people who identify as LGBTQI+, immigrants, and those associated with sexual crimes face unique stigma. Key recommendations include increasing access to and the capacity of services specific to intersectional groups and conducting longitudinal research.