As the Obama administration's top Supreme Court lawyer, Kagan has argued six cases before the people who will become her colleagues if she wins Senate confirmation.
In nominating Kagan to replace Justice John Paul Stevens, President Barack Obama has chosen a brilliant legal scholar with liberal views and conservative friends. Kagan, 50, already has won Senate confirmation once, after Obama nominated her to be solicitor general, the administration's top Supreme Court lawyer.
Kagan's reputation for bringing together liberals and conservatives on Harvard's notoriously fractious law school faculty appears to hold the key to her rapid rise.
As dean of the Harvard Law School, Kagan's hiring of young conservative scholars "sent a strong signal to conservative alumni that, despite her own party affiliation, she was committed to intellectual diversity and meritocracy at the law school," said Harvard alumnus and former Bush administration lawyer Brad Berenson.
Laurence Tribe, the noted liberal law professor at Harvard who now is a Justice Department official, called the school "an almost ungovernable place." Tribe is on leave from the law school.
"In the 40 years I've been on the law faculty, it has never been as effective and enthusiastic a place as it is now," Tribe said last year in assessing Kagan's time as dean. "That's a result of her insights and political savvy."
When Kagan took over as the first female law dean at Harvard, she called the challenge exciting and scary -- "but scary in the way that all exciting things are scary." And she pledged to draw on the political and people skills she had developed while serving in government.
Her belief in the power of government was there early on.
The quotation she selected to run with her photo in the Hunter College high school yearbook in 1977 was from former Supreme Court Justice Felix Frankfurter.
It read: "Government is itself an art, one of the subtlest of arts,"
Kagan also showed a lighter side by selecting a quotation from Mark Twain's "Huckleberry Finn:" "Persons attempting to find a motive in this narrative will be prosecuted; persons attempting to find a moral in it will be banished; persons attempting to find a plot in it will be shot."
Kagan is now the first woman to serve as solicitor general, and she would be only the fourth woman to serve on the Supreme Court.
She would be the youngest justice -- 40 years younger than Stevens and five years behind Chief Justice John Roberts.
Kagan would be the fifth solicitor general to move to the high court, but her ascent from one job to the other would be the fastest, outstripping even her barrier-shattering onetime boss, Marshall.
President Bill Clinton nominated her to the federal appeals court in Washington in 1999, but the Republican-controlled Senate never acted on the nomination.
Liberal interest groups were not thrilled when Kagan publicly supported a couple of President George W. Bush's appeals court nominees, but criticism of Kagan from the left could be blunted in part because Obama could have additional high court vacancies to fill.
Social conservatives, on the other hand, already have sought to paint her as "disturbingly out of the mainstream" on some issues, including her opposition to the military's "don't ask, don't tell" policy for gay soldiers.
Kagan argued strenuously against the policy, calling it "just flat out wrong."
She was among law school deans who filed a brief in a Supreme Court case over a federal law that withholds government money from colleges that ban the military from recruiting on campus because of objections to the Pentagon's policy on gays. The Supreme Court upheld the law unanimously.
Last year, the Senate confirmed Kagan by a vote of 61-31, with only 7 Republicans supporting her. The relatively large number of votes against her cheered some conservative activists, although the margin suggested Kagan would again prevail in a confirmation vote for the Supreme Court.
One academic paper she wrote in the 1990s could be used against her in the confirmation process. Kagan lamented the lack of "seriousness and substance" in confirmation hearings for Stephen Breyer and Ruth Bader Ginsburg. "When the Senate ceases to engage nominees in meaningful discussion of legal issues, the confirmation process takes on an air of vacuity and farce," she wrote in the University of Chicago Law Review in 1995.
Asked about this by senators when her nomination as solicitor general was pending, Kagan replied that she is "less convinced than I was in 1995 that substantive discussions of legal issues and views, in the context of nomination hearings, provide the great public benefits I suggested."