More recently, the prolonged grief disorder (PGD) has been recognized as a mental health disorder following bereavement, which is distinct from depression and PTSD. However, the number and proposed symptom items vary across the ICD-11 and the DSM-5-TR criteria for PG. The Traumatic Grief Inventory-Self Report Plus (TGI-SR+), which is an updated version of the TGI-SR, is currently the only robust instrument that assesses PG according to the ICD-11 and DSM-5-TR criteria. For research and clinical use among French-speaking countries, the forward-backward procedure was applied to translate the TGI-SR+ into French language. Exploratory factor analysis and parallel analysis converged towards a two-dimensional structure for the TGI-SR+, representing adaptation difficulties and traumatic separation distress. However, items mapping onto ICD-11 and DSM-5-TR criteria for PG represented a one-dimensional structure. Findings based on item response theory method provided strong evidence for discriminative characteristics of the items. The internal reliability was excellent for the TGI-SR+ (McDonald’s ω = 0.97) and ICD-11 and DSM-5-TR criteria for PGD (McDonald’s ω = 0.95). We also demonstrated a very high temporal stability for the TGI-SR+ total score (ICC = .91, p < 0.0001) and ICD-11 PGD and DSM-5-TR PGD (ICC = 0.90, and ICC = 0.88, ps < 0.0001, respectively). The concurrent validity of the instrument was also demonstrated, such that the TGI-SR+ total score and all combinations were positively and significantly associated with the levels of depression, anxiety and post-traumatic stress symptoms. However, the effect sizes were moderate. We conclude that for research and clinical use among French bereaved populations, the TGI-SR+ is a sound tool with very good psychometric properties.