Objectives: This study aimed to fill the data gap regarding the prevalence of germline (g) BRCA1/2 mutations in patients with metastatic breast cancer (mBC) in France. Methods: A prospective gBRCA1/BRCA2 mutation analysis was proposed to all patients with mBC treated in seven French centers between 19 February and 30 November 2015. The BRCA TrueTM test (Pathway Genomics^®, San Diego, CA, USA) analyzed the coding and flanking regions of BRCA1 and BRCA2 genes using next-generation sequencing, Sanger sequencing, and multiplex ligation-dependent probe amplification. Results: Among 407 included mBC patients, 11 (2.7%) carried pathogenic gBRCA1/2 mutations. Of these, five (45%) would not have met standard criteria for genetic screening. Compared with non-carriers, gBRCA1/2 carriers were significantly younger at mBC diagnosis (47.5 vs. 60.7 years, p = 0.0006), had higher-grade tumor histology (p = 0.044), and had a higher rate of contralateral recurrence (36.4% vs. 11.6%, p = 0.035), with comparable adjusted survival (median overall survival 74.9 vs. 100.1 months, p = 0.97). Variants of uncertain significance were identified in 17 (4.2%) patients. Conclusions: The 2.7% prevalence of gBRCA1/2 mutations in this prospective French mBC cohort was relatively low. Nearly half of the mutation carriers would not have been routinely referred for oncogenetic counseling, underscoring the potential value of broader genetic screening in this population.