The 'Someone Like You' singer's second LP broke the four million sales barrier at the weekend when it reached number one on the UK album chart for a 21st week.
21's sales total currently stands at 4,020,000 - nearly 61,000 more than Jackson's classic 1987 record, which features the iconic tracks 'Man In The Mirror', 'Smooth Criminal', 'The Way You Make Me Feel' and 'Dirty Diana'.
"This is another incredible achievement to cap a year of incredible achievements for Adele," said Martin Talbot of the Official Charts Company. "By overtaking Bad, 21 has truly, officially cemented Adele's place among the all-time greats.
"Who would bet against her improving further on that achievement by taking steps towards the all-time Top 5?"
21 is presently the eighth biggest-selling album of all time in the UK. Its nearest competition is The Dark Side Of The Moon by Pink Floyd with 4,114,000 copies and Brothers In Arms by Dire Straits, which stands at 4,152,000.
Queen's Greatest Hits collection currently sits atop the UK's best-sellers chart with sales of 5,863,000.
In December, Adele's 21 overtook Back To Black by the late Amy Winehouse to become the biggest-selling album of the 21st century in the UK.
It has been confirmed that since Adele's performance and awards victory at the Brits last Tuesday (February 21), a copy of either 21 or her debut album 19 is purchased on average every seven seconds.
Watch Adele perform 'Rolling In The Deep' at the Brit Awards below: