Yet another submission to the MHS competition – which ended in January 2017 with the selection of the SIG Sauer P320 as the new M17/M18 MHS service pistol for the U.S. Armed Forces – reaches the global commercial and professional markets: the FN 509 is FN's latest 9mm Luger, semi-automatic, polymer-frame, semi-automatic pistol. Accoreding to the company, the FN 509 was "born out of the company’s effort to produce a contender for the U.S. Army’s Modular Handgun System (MHS) competition and has been further enhanced to meet the needs of U.S. law enforcement and commercial customers".

When the requirements for MHS were released, the FN engineering team took the successful elements of the company's own FNS Compact and further developing those to meet the needs of the U.S. Army’s solicitation for a new, full-size pistol; between the submission of MHS and the commercial release of the FN 509, FN America LLC. worked with law enforcement agencies throughout the U.S. and captured on-site feedback used to further optimize the pistol.

FN made changes internally and externally to the FNS Compact architecture to meet the rigorous performance standards of the MHS requirements and further developed the platform into the FN 509 with help from industry experts. Over the course of development, the platform has been tested extensively for reliability, ammunition compatibility and durability – totaling more than 1 million rounds. Aesthetic changes to the platform include the aggressive cocking serrations, enhanced grip textures, guarded controls and recessed target crown on the barrel.

Critical internal components were completely redesigned to ensure maximum performance to meet FN’s demanding standards.

The FN 509 is a blowback-operated, striker-fired design features a set of passive safeties (no manual safety available), a DAO trigger ranging between 5.5 and 7.5 pounds (2,5 / 3,5 kg) in weight; the slide features a set of three-dot luminescent or night sights, and the issued double stack magazines hold 17 rounds – although 10-rounds magazines are available for jurisdictions with magazine capacity restrictions. 7.4 inches (18,8 cm) long overall, the FN 509 features a four-inch barrel and weighs 26.9 oz (762 grams) unloaded.