His 2010 release Recovery has now shifted 1,001,000 copies, according to Nielsen SoundScan.
In total, more than 3.9 million copies have been sold.
Vice chairman of Eminem's record label Interscope Steve Berman described the achievement as "incredible".
"I have had the pleasure of working with Eminem throughout the course of his career, and I'm delighted to be a part of yet another milestone on his amazing journey," he said.
Eminem earlier this year was awarded with two Grammys and a prize for best rap album.
Continued steady sales will see Adele become the second artist to hit the landmark in the US with her album 21 "next week".
