NPD Group's June figures confirm that the handheld console reached the milestone after just over a year on the market, MCV reports.
Nintendo is planning to release a larger iteration of the device, the 3DS XL, in August alongside blockbuster title New Super Mario Bros 2. New entries in the popular Paper Mario and Luigi's Mansion series are also on the way.
"Nintendo 3DS is entering the next phase of its life cycle with new hardware, new games and proven franchises. This milestone shows we've got a great foundation to build from," said Nintendo sales executive Scott Moffitt.
"The game lineup for Nintendo 3DS last holiday season was one of the strongest in our history.
"We're poised to top it this year. Every week, gamers will have the best franchises in the world in a glasses-free 3D experience that can't be found anywhere else. Add Wii U into the mix and it's a great time to be a Nintendo fan."
The gaming giant also announced that The Legend of Zelda: Ocarina of Time 3D has sold more than 1 million units domestically, a feat previously achieved by Super Mario 3D and Mario Kart 7.
Photo gallery - Hands on with the Nintendo 3DS XL:
Copyright: Digital Spy