During the evening of 13 November 2015, the deadliest terror attacks in France in recent times occurred in the Paris area. Overall, 130 people were killed, 643 were physically injured and several thousands were psychologically impacted. Thousands of first responders, including health professionals, firefighters, affiliated volunteers and police officers were mobilized that night and during the subsequent weeks. The aims of our study were to measure the psychological impact on first responders in terms of post-traumatic stress disorder (PTSD) and partial PTSD as well as associated factors 12 months after the 13 November 2015 terrorist attacks. First responders who had intervened during the night and/or the aftermath of the terror attacks had the possibility of answering a web-based study 8-12 months after the attacks. They satisfied criterion A of the DSM 5 definition of PTSD. PTSD and partial PTSD were measured using the PCL-5. Gender, age, educational level, exposure, first responder category, mental health and traumatic event history, training and social support were all analysed as potential factors associated with PTSD and partial PTSD, using multinomial logistic regression. Overall, 663 participants were included in this analysis. Prevalence of PTSD in our sample went from 3.4% among firefighters to 9.5% among police officers and prevalence of partial PTSD from 10.4% among health professionals to 23.2% among police officers. Low educational level and social isolation were associated with PTSD and partial PTSD. Intervention on unsecured crime scenes and lack of training were associated with PTSD. Special attention should be given to first responders living in social isolation, those with low educational levels and those who intervene in unsecured crime scenes. Education and training about the potential mental health consequences of mass trauma intervention should be developed.