Stenotrophomonas maltophilia is an intrinsically multi-drug resistant (MDR) bacterium initially found in the environment that is emerging worldwide. The rate of isolation from immunocompromised patients combined with limited treatment options make S. maltophilia a new concern in clinical settings. Here we report the first detection of the Metallo-β-Lactamase (MBL) gene bla IMP-15 in S. maltophilia isolated from a patient in Lebanon. The isolate exhibited an extensively drug-resistant profile with high resistance to trimethoprim-sulfamethoxazole, levofloxacin, and minocycline considered by the Clinical and Laboratory Standards Institute (CLSI) as first-line antimicrobials used to treat such infections. Resistance to newly adopted anti- S. maltophilia agents was noted such as ceftazidime-avibactam. However, the isolate only showed susceptibility to cefiderocol and synergy was observed upon treatment with a combination of ceftazidime-avibactam and aztreonam by disk diffusion. Long-read and short-read whole-genome sequencing was performed and generated a hybrid assembly of 8 contigs. The isolate belonged to strain T50-20 and showed a novel sequence type. Moreover, several antimicrobial resistance genes conferring resistance to multiple antimicrobial classes were found. Particularly, bla IMP-15 was detected on insertion sequence IS6100 surrounded by transposition elements. Furthermore, the presence of the IMP gene was confirmed by polymerase chain reaction (PCR) followed by agarose gel electrophoresis and Sanger sequencing. This study highlights that the threat behind the bla IMP-15 gene is not only linked to the high resistance to Ceftazidime-avibactam in the S. maltophilia isolate but is also of concern due to its transmissibility to other pathogens, conferring alone an MDR profile.