Mr Hollande ended his seven-year relationship with Ms Trierweiler after his affair with an actress was revealed in January. The 49-year-old journalist vowed at the time she would not keep quiet, breaking with a French tradition of maintaining discretion over private lives in politics.
The 320-page book is laced with unflattering references to Mr Hollande as cold or callous. But the charge that he ridiculed the poor was the one that sparked most media debate given his efforts to portray himself as aware of the plight of the needy.
"He presented himself as a man who disliked the rich," Ms Trierweiler, a journalist with glossy magazine Paris Match, wrote of Mr Hollande's successful 2012 election campaign.
"In reality, the president doesn't like the poor. In private, this man - the left-winger - calls them 'the toothless' and is so pleased at how funny he is."
Mr Hollande's Elysee Palace has refused to comment on the book. But, in an unexpected turn, it was Segolene Royal, the mother of Mr Hollande's four children and the woman he left for Ms Trierweiler, who sprang to his defence.
"This is the opposite of what he stands for," Ms Royal, herself a former presidential candidate who is now his energy minister, said, calling the accusation "total nonsense".
When he won power in 2012, Mr Hollande, 60, marketed himself as a "Mr Normal" president whose car would stop at red traffic lights like everyone else's and said he would shun the claimed ostentation of his conservative predecessor, Nicolas Sarkozy.
While he this year took a more centrist course, he still insists social justice is at the core of his government's policies.
Yet with the economy stuck in a rut and unemployment increasing to around 10 per cent, his popularity rating has sunk to the lowest of any post-war leader.