Former US president Barack Obama reportedly twice asked a previous girlfriend to marry him before meeting his current wife, Michelle, a new book claims.

Rising Star: The Making of Barack Obama, by David J. Garrow, carries the comments of a former love interest of the politician, Sheila Miyoshi Jaher.

Jaher, who lived with Obama in Chicago, claims in the book that he fell in love with her just as he began his meteoric career in politics, and that he proposed on two separate occasions.

"In the winter of '86, when we visited my parents, he asked me to marry him," Jaher told the book's author, also adding she told Obama: "Not yet."

Jaher also details the moment she realised Obama had become serious about a career in politics.

"He became ... so very ambitious, very suddenly," she says in the book, in comments carried by the Washington Post.

"I remember very clearly when this transformation happened, and I remember very specifically that by 1987, about a year into our relationship, he already had his sights on becoming president."

She adds that Obama continued to meet up with her for a year at the beginning of his relationship with Michelle Obama, nee Robinson, the Telegraph reports. In the book, she says: "I always felt bad about it."

The biography details relationships Obama had with several previous girlfriends prior to meeting Michelle at Harvard, where the pair studied.

It also mentions his use of cocaine – something that the politician has admitted to previously, writing about his experimentation with drugs during his younger years.

Rising Star: The Making of Barack Obama is published on 9 May.