The 'No Love' rapper broke the record with his latest album Recovery, which was released in June 2010.
The album's digital sales currently stand at 1,001,000 copies, while combined sales with the physical edition equal 3.9 million, according to Billboard.
Interscope Records vice-chairman Steve Berman commented: "Recovery selling one million digital albums is an incredible achievement by an incredible artist. 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."
Adele is also on course to become the first British artist to sell over one million digital copies of a single album with her second record 21.
The 'Set Fire To The Rain' songstress is expected to pass the sales milestone next week, with her sophomore effort still riding high on the Billboard 200 chart.
Eminem recently faced criticism regarding his new music video for Recovery single 'Space Bound', in which he depicts a man with a split personality committing suicide.
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Watch the music video for Eminem's 'Space Bound' below: