As a longtime family friend, the director Mike Nichols, said, it’s a job for which Ms. Kennedy is ideally suited. After all, he said, “In the course of her life, what has she learned if not diplomacy?”

The position is a particularly interesting one for Ms. Kennedy, a crucial supporter of President Obama during the 2008 campaign. Unlike other high-profile postings like those in London and Paris, which have often been filled with prominent social figures (Kingman Brewster Jr., Pamela Harriman) or prodigious fund-raisers (Arthur Watson, Charles H. Rivkin) or both (Walter H. Annenberg), the one in Tokyo has often been for notable politicians nearing the end of their careers (Mike Mansfield, Thomas S. Foley, Walter F. Mondale and Howard Baker, to name a few), a testament to the importance of Japan as an ally and the premium that society places on status. (The current ambassador is John V. Roos, a lawyer and major fund-raiser for President Obama.)

In addition to describing her as a person who has written several “wonderful” books and dedicated herself to public service, Mr. Mondale, the vice president under Jimmy Carter and the ambassador to Japan from 1993 to 1996, said that Ms. Kennedy’s famous last name should serve her well.

“The Japanese will be thrilled with this news,” he said in a phone interview. “She will be very popular. They love the Kennedys over there. They’ve worked with several of them, and they appreciate their position in public life. They know she’s an American star, and they know she’s a serious person and that she’ll be well prepared. It will be a strong embassy under her leadership. I think they’re honored.”