A two-piece snap-on magazine adapter for a handgun. This magazine adapter provides a relatively continuous surface between the handgun and locked extended length magazine to afford the handgun user with a comfortable grip among other benefits. In the preferred embodiment, the magazine adapter has two snap together pieces: a main body and an end cap. The main body has an interior pocket configuration contoured to capture the magazine floor plate. The main body of the device is then captured by an end cap that locks via a detent mechanism onto the main adapter body. The magazine adapter fits completely around the magazine such that when the magazine is locked into the handgun, the resulting grip provides a smooth, continuous and comfortable fit between the extended length magazine's floor plate and the butt of the handgun's grip. The magazine adapter of the present invention may be adapted to fit a variety of handgun models desirous of using extended length magazines without any modification of the magazine itself.