Background: Humanitarian workers operate in traumatic contexts, putting them at an increased risk of adverse mental health outcomes. The quality of the support they receive from their organization, their supervisor, and team members are proposed as determinants of mental illness and well-being, via the stress-appraisal process. Objective: Grounded in organizational support theory, we sought to understand the relationship between organizational factors, including perceived organizational support, supervisor support, and team support, and indicators of both adverse mental health and mental well-being among humanitarian volunteers. This relationship is hypothesized to be mediated by the perceived psychological stress. Methods: A sample of 409 humanitarian volunteers from the Sudanese Red Crescent Society completed an online, anonymous, survey comprised of the Perceived Supervision, Perceived Organizational Support, Team Support, and Perceived Psychological Stress scales, as well as the Generalized Anxiety Disorder and Patient Health Questionnaire scales, (GAD-7 and PHQ-8), and the Warwick-Edinburgh Mental Well-being Scale. Study objectives were tested using structural equation modelling (SEM) procedures. Results: Perceived helplessness (PH) and perceived self-efficacy (PSE), as measures of psychological stress, were both found to fully mediate the relationship between perceived organizational support and mental health outcomes. Perceived organizational support was associated with PSE and inversely with PH. PH was associated with adverse mental health and inversely related to mental well-being. PSE was only associated with mental well-being. Perceived supervision was negatively associated with PSE. Conclusions: Perceived organizational support is a key determinant of the mental health of humanitarian volunteers, with greater perceived support associated with lower distress symptomology and greater mental well-being. Humanitarian agencies should take actions to improve their internal organization support systems to mitigate the stress associated with working in traumatic contexts. Specifically, more attention should be paid to the organizational support of the volunteers as front-line workers in humanitarian settings. Cuidando la salud mental de los voluntarios humanitarios en contextos traumáticos: La importancia del apoyo organizacional Antecedentes: Los trabajadores humanitarios operan en contextos traumáticos, lo que los pone en un mayor riesgo de resultados adversos para la salud mental. La calidad del apoyo que reciben de su organización, su supervisor, y los miembros del equipo han sido propuestos como determinantes importantes de las enfermedades mentales y el bienestar, a través del proceso de evaluación del estrés. Objetivo: Basados en la teoría del apoyo organizacional, buscamos comprender la relación entre los factores organizacionales, incluyendo el apoyo organizacional percibido, el apoyo del supervisor, y el apoyo del equipo, y los indicadores de salud mental adversa y bienestar mental entre los volunta...