An anti-rotation thumb rest providing advantages that allow for non-destructive and unobtrusive installation on firearms that would otherwise not be able to accommodate a thumb rests. The thumb rest may be constructed by attaching or manufacturing a long cylindrical pin onto the back side of a thumb rest, as to serve as a trigger pin, locking block pin, or other pin used for securing pistol components internally together, while also providing a typically rectangular, square, circular, or irregular shaped protrusion that serves as an anti-rotation stop for installation in a typically unused recess in the firearm's receiver, that was not expressly designed for installing components.