Caroline Kennedy said she hoped to carry on the legacy of her murdered father John F. Kennedy by serving as the US ambassador to Japan.
Kennedy, a strong supporter of President Barack Obama, appeared before a Senate panel on Thursday as she sought confirmation for her most public role since she was a playful young girl in the White House from 1961-63.
"I can think of no country in which I would rather serve than Japan," said Kennedy.
The 55-year-old said she first visited Japan in 1978 with her uncle, the late senator Ted Kennedy, and was "deeply affected by our visit to Hiroshima", which the US obliterated in the world's first atomic bombing in 1945.
Kennedy called Japan "an indispensable partner in promoting democracy and economic development." She added: "These are areas I care deeply about and, if confirmed, I will work to further strengthen this critical partnership at a vital moment in its history."
The Senate appeared virtually certain to confirm Kennedy, meaning that she would head to Tokyo before November 22 - the 50th anniversary of her father's assassination, when she was five days short of her sixth birthday. "This appointment has a special significance as we commemorate the 50th anniversary of my father's presidency," she said. "I would be humbled to carry forward his legacy in a small way and represent the powerful bonds that unite our two democratic societies," she said.
Kennedy said her father, who was seriously wounded by a Japanese destroyer in the second world war, had hoped to pay the first US state visit to Tokyo.
Gerald Ford eventually became the first US sitting US president to travel to Japan in 1974.
Kennedy would be the first woman US ambassador to Tokyo and hinted she would highlight women's rights in Japan, which ranks lower than most developed countries on sexual equality in the workplace.
"As a woman, I have opportunities in Japan to represent the United States and the progress we have made here," she said.
While no senators opposed Kennedy, several US foreign policy experts have criticised the nomination, saying she has little experience at a time that Japan is managing high tensions with a rising China and an often bellicose North Korea.
She said the US took no position on the ultimate sovereignty of the Diaoyu Islands claimed by Beijing - known as the Senkakus in Japan - but "we do recognise they are under Japanese administration" and are covered by a US-Japan security treaty.