Barack Obama proposed to a "serious" girlfriend before he met his eventual wife Michelle, according to a new biography of the former US President.

The book - "Rising Star: The Making of Barack Obama" writtedn by David J. Garrow - shares for the first time the story of the woman Sheila Miyoshi Jager, with whom Obama lived in Chicago, The Washington Post said in a review on Wednesday.

Jager is now a professor at Oberlin College, Ohio.

Jager told Garrow: "In the winter of ‘86, when we visited my parents, he asked me to marry him".

However, her parents objected to the union, believing her to be too young, as she was in her early 20s and two years younger than Obama.

But they continued living together.

In early 1987, when Obama was 25, she sensed a change.

"He became. . . so very ambitious very suddenly...by 1987, about a year into our relationship, he already had his sights on becoming president," Jager told the author.

Obama eventually asked Jaeger to marry him again before he departed for Harvard Law School. He wanted her to come with him despite their "increasingly fraught relationship".

After his first year at Harvard, Obama returned to Chicago as an associate at a prestigious local law firm. There he met Michelle Robinson, the future First Lady and an employee at the firm. Their relationship quickly became serious.

In the book, Garrow also writes about how Obama lived, and explored the calculations he made in the decades leading up to his winning the presidency.

"Every step - whether his foray into community organising, Harvard Law School, even the choice of whom to love - was not just about living a life but about fulfilling a destiny."

Garrow, who received a Pulitzer Prize for his biography of Martin Luther King Jr., concludes this massive new work with a damning verdict on Obama's determination: "While the crucible of self-creation had produced an ironclad will, the vessel was hollow at its core."