A firearm retention mechanism is provided for a holster. The device comprises first and second arms that each have a first end and a second end, outwardly extending retention elements and trigger guard stops, and a fastener which connects the first and second arms so that they define an open top, with the retention elements and trigger guard stops facing one another, the trigger guard stops located below the retention elements. The arms are connected to sides of the holster with the open top facing upwardly to receive a trigger guard of the firearm, which is then pressed between the retention elements.