<p>The engagement of former extremists/formers in preventing and countering violent extremism (P/CVE) within the correctional settings has increased over the years. This is mainly because formers are perceived as a credible voice whose involvement can enhance the credibility of P/CVE efforts in prison and after release. However, very few studies have examined what constitutes “credible formers,” especially in the Indonesian context. This article will examine what makes formers credible based on 13 semi-structured interviews with terrorist inmates, prison officers, former terrorist inmates, parole officers, and one civil society organization (CSO) representative; three focus group discussions; and desk studies. The findings suggest that a former’s credibility is built on religious understanding, combat or battlefield experience, and a significant position within a group or movement. In addition, the ability to convey a transformative message supports credibility. However, it is very important to note that the involvement of formers in P/CVE must be preceded by thorough preparation and an assessment of the formers’s compatibility with the convicted terrorist. Failure to do so could jeopardize formers’s safety.</p>