Caroline Kennedy is expected to be nominated U.S. ambassador to Japan, but the nomination is not yet finalized, a knowledgeable source told ABC News Monday.

Kennedy, the only living child of President John F. Kennedy, is a lawyer and author of 10 books, including a text on the Bill of Rights and a collection of her mother's favorite poems.

In the past election cycle, Kennedy campaigned for President Obama at several events in swing state New Hampshire. She contributed to the Obama campaign narrative that Mitt Romney would have been the wrong candidate for women.

She endorsed Obama back in January 2008 in an op-ed that compared him to her father. During the 2008 election, she led the effort to pick Vice President Joe Biden.

She was strongly considered to be next in line to take Hillary Clinton's Senate seat in New York when she withdrew to serve as secretary of state in January 2009, but at the last minute, Kennedy took herself out of consideration for that position, because of a "very private family matter." A book about the life of her uncle, Ted Kennedy, suggests her children might have been the reason she opted out.

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The 55-year-old Kennedy daughter is largely considered one of the more private members of the politically prestigious family.

Kennedy has recently served as the president of the Kennedy Presidential Library and an adviser to the Harvard Institute of Politics.

John Roos has served as U.S. ambassador to Japan since August 2009. He was the first in that role to attend the Hiroshima Peace Memorial Ceremony, remembering the horrors suffered after the dropping of the atomic bomb. Other ambassadors to Japan have included John "Tom" Schieffer, brother of "Face of the Nation" anchor Bob Schieffer, and former White House Chief of Staff Howard H. Baker.