Michelle Obama's memoir Becoming looks set to become the biggest-selling autobiography ever after it sold 10 million copies globally in just five months, according to its publisher.

"We believe this could be the most successful memoir in history," Thomas Rabe, the CEO of Bertelsmann SE, the parent company of book publisher Penguin Random House, told reporters in Berlin, where Bertelsmann is based.

The publisher paid $60 million to Obama and her husband, Barack, the former president of the United States, for rights to a book written by each of them after they left the White House in 2017.

Markus Dohle, Penguin Random House's CEO, said that he hoped to release Obama's memoir about his presidency later this year.

Bertelsmann owns 75 percent of New York-based Penguin Random House. Sales of Obama's book lifted total sales at the German media giant to $20 billion, the highest since 2007, Bloomberg reports.

The former first lady, 54, released the memoir about her journey from Chicago's South Side to the White House in November and it quickly became a best-seller.

In its first week of publication, Becoming sold more than 1.4 million copies, Penguin Random House said last year. The sales include print, audiobooks and digital copies sold worldwide.

NPD Group, a market research firm, said that Becoming already ranked as the second-highest selling memoir by the number of printed copies sold in the US.

Obama has had a highly successful arena tour in the US promoting her book and will travel to Canada, the UK, Paris, Amsterdam and Sweden for further promotional events.

In the memoir, Obama chronicles experiences that have shaped her from childhood to becoming an attorney and balancing the demands of motherhood to her time as first lady from 2009 to 2017.

She is frank about problems she had in her marriage with Obama and her struggles with infertility and the use of in vitro fertilization (IVF) to conceive daughters Malia and Sasha, now 20 and 17, respectively.

Chi John, 35, from Brooklyn, New York, said that she went to see Obama on her book tour at the Barclays Center in Brooklyn on Dec 19. She told China Daily: "I was surprised that she was so candid in her book about her marriage and the fact that she had IVF. I didn't expect her to be so honest. She was really open. I respected that. I was already a fan, but I thought her book was awesome."

"I bought the book because I see her as a role model. I wanted to read all about her life. I just love her!'' Natania Phillips, 42, from northwest London told China Daily. "She shows what's possible with hard work regardless of your color. I intend to go and see her on her book tour when she visits London next month.''

In her book, Obama also criticizes President Donald Trump, writing that she could "never forgive him" for "putting my family's safety at risk" over the birther movement – in which conspiracists claimed he was born in Kenya, not the US.