A flexible adjustable trigger plug is a device that is utilized to prevent the accidental pressing and subsequent discharge of a firearm trigger. The device features a plug that may be fitted behind the trigger as well as a first lip and a second lip that are able to hold the plug in place behind the trigger. A first concave cavity and a second concave cavity are present as well in order to facilitate insertion and removal of the device by pressing. The device serves as a physical obstruction that prevents the trigger from being accidentally pressed. The device is flexible and may be adjusted by turning the device when in place behind the firearm trigger, allowing the device to be utilized with a wide variety of firearms. The device may feature a lanyard arch and opening that allow a lanyard clasp or clip to be secured to the device.