Michelle Obama's memoir is on course to become the most popular autobiography to date, according to its publisher.
Becoming, first published just five months ago, has already sold more than 10 million copies, Bertelsmann said.
"We believe that these memoirs could well become the most successful memoir ever," said Thomas Rabe, chief executive of the German firm.
The firm paid $60m (£48m) in 2017 for the rights to the book alongside that of former US President Barack Obama.
Mr Obama's book is yet to be published.
Bertelsmann owns a 75% stake in Obama publisher Penguin Random House.
Nielsen - which tracks UK book sales - said Michelle Obama's book was currently 11th on its list of top 20 bestselling biographies and memoirs, which tracks sales since official records began in the late nineties.
A Child Called It, by Dave Pelzer is the top selling autobiography in the UK. The book has sold 1.1 million copies, compared to 618,000 in the UK so far for Becoming.
Michelle Obama's book, which explores her experience from childhood, her work, motherhood and her time in The White House, has been praised for its universal appeal across genders and ages.
In it, she reveals difficulties in her marriage with Barack, disclosing details of how the couple suffered a miscarriage and later used in vitro fertilisation (IVF) to conceive both children, Malia and Sasha.
The 54-year-old also criticises the current US President, Donald Trump, writing that she can "never forgive" him for "putting my family's safety at risk" over his championing of the "birther" theory that her husband was not born in the US and thus was not a legitimate president of the US.