TOKYO — For decades, she has been a Japanese woman breaking barriers.

As a young television newscaster fluent in Arabic, she interviewed the Libyan dictator Col. Muammar el-Qaddafi. When she asked sharp questions of a future prime minister, he recruited her to run for Parliament, and she won. As environment minister, she pushed traditionally formal Japanese businesses to let workers wear casual clothes in the summer to lower air-conditioning bills. During Prime Minister Shinzo Abe’s first stint in the post, she became the first woman to be named defense minister, and though felled by a scandal, she returned last year to become the first female governor of Tokyo.

Now Yuriko Koike is shaking things up again.

Ms. Koike founded a new national party two weeks ago, and Japan is watching to see whether she goes for broke and runs for parliamentary office herself in elections this month, which would put her in position to challenge Mr. Abe.

Ms. Koike, 65, who was elected governor of Tokyo just over a year ago, has made no secret of her ambition to become Japan’s first female prime minister. This month’s lower-house election, called early by Mr. Abe in an effort to consolidate his power, provides an opportunity for her.

So far, Ms. Koike has insisted that she will not run for national office. “I was given a passionate offer, but as I have repeatedly said, I don’t have any intention to run in the lower-house poll,” she told reporters as recently as Thursday.