Background First responders (FRs) are frequently exposed to potentially traumatic events, including terror attacks, and may consequently be at risk of developing mental health disorders. Prior research suggests that FRs with mental health disorders often do not receive appropriate treatment. More knowledge is needed about their use of mental health care (MHC). Aims This study aimed to identify factors associated with receiving immediate support, post-immediate support and engagement in MHC among FRs of the November 2015 terror attacks in Paris. Methods A web-based study was conducted 8-12 months after the attacks on 663 FRs who were mobilized during the night and/or the aftermath of the attacks. Logistic regression was performed to analyse factors associated with MHC. Results Overall, 44 FRs sought MHC. Among FRs with post-traumatic stress disorder (PTSD), partial PTSD or depression (n = 60), 38% sought MHC (n = 23). Post-immediate support was associated with immediate support, and both were associated with knowing someone who could help regarding the potential psychological risks following a traumatic event. MHC engagement was associated with a history of MHC, post-immediate support and the presence of PTSD, partial PTSD or depression. Conclusions Among FRs with PTSD, partial PTSD or depression, few sought MHC. Improved access to MHC for FRs after terror attacks is essential. Knowing someone who could help regarding potential psychological risks may facilitate immediate and/or post-immediate support. Furthermore, postimmediate support could encourage engagement in MHC. Efforts should be made before and after potentially traumatic events to ensure mental health education for FR.