Background Post-traumatic growth (PTG) refers to beneficial psychological change following trauma. Aims This study explores the sociodemographic, health and deployment-related factors associated with PTG in serving/ex-serving UK armed forces personnel deployed to military operations in Iraq or Afghanistan. Method Multinomial logistic regression analyses were applied to retrospective questionnaire data collected 2014–2016, stratified by gender. PTG scores were split into tertiles of no/very low PTG, low PTG and moderate/large PTG. Results A total of 1447/4610 male personnel (30.8%) and 198/570 female personnel (34.8%) reported moderate/large PTG. Male personnel were more likely to report moderate/large PTG compared with no/very low PTG if they reported a greater belief of being in serious danger (relative risk ratio (RRR) 2.47, 95% CI 1.68–3.64), were a reservist (RRR 2.37, 95% CI 1.80–3.11), reported good/excellent general health (fair/poor general health: RRR 0.33, 95% CI 0.24–0.46), a greater number of combat experiences, less alcohol use, better mental health, were of lower rank or were younger. Female personnel were more likely to report moderate/large PTG if they were single (in a relationship: RRR 0.40, 95% CI 0.22–0.74), had left military service (RRR 2.34, 95% CI 1.31–4.17), reported better mental health (common mental disorder: RRR 0.37, 95% CI 0.17–0.84), were a reservist, reported a greater number of combat experiences or were younger. Post-traumatic stress disorder had a curvilinear relationship with PTG. Conclusions A moderate/large degree of PTG among the UK armed forces is associated with mostly positive health experiences, except for post-traumatic stress disorder.