The singer was presented with a placard to mark the achievement at a recent gig, which counted Who You Are's worldwide sales along with those of its singles.
High sales of her hits 'Price Tag', 'Nobody's Perfect' and 'Domino' helped toward the final figure, with a multitude of further record sales due to be counted in the coming months.
Jessie J follows Adele as one of the best-selling female artists from the UK over the past 12 months. Since its release last March, Who You Are has reached the Top 20 in over 10 countries.
Meanwhile, the singer plans to work on tracks for the follow-up to her debut album over the next couple of weeks, ahead of her commitments on the forthcoming Voice UK live shows.
"Stuuuuddddioooooo aaaghhhjkgferyiojkcvsuiojxswef for 2 weeks!!!!" she tweeted. "Album two begins.... I'm going IN! Let's go!"
Jessie J will officially release 'LaserLight' as her next single in the UK on May 13.
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Watch the video for Jessie J's 'LaserLight' below: