She graduated from Shaker Heights High School in Cleveland, Ohio, in 1935 and earned a degree in political science from Swarthmore College in Pennsylvania in 1939.

In the interwar era, she was active in the Pan-Pacific Women's Association and attended several youth conferences aimed at developing international cooperation.

Near the end of the war, she became an editor at the Japanese office of Reader's Digest and began working as an interpreter and translator for foreign correspondents, including Keyes Beech and Edgar Snow.

When her leftist associations began to impact her ability to publish, Matsuoka returned to the United States and completed graduate studies in foreign relations at Swarthmore and then at the Fletcher School of Law and Diplomacy between 1949 and 1952.

Matsuoka worked with women's groups to create pan-Asian solidarity and closer alliances between Japan and nations in the Global South.

[3][6] Masao was the brother of Japan's first woman journalist, Motoko Hani,[3][7] who employed Hisa upon her return from the United States in 1912 and introduced the couple.

[14] In 1927, Matsuoka's family moved to Seoul, Korea,[12][15] when her father agreed to accept an appointment as vice president of the Japanese-government-run newspaper Keijō Nippō.

[4] The conference was designed to bring women's rights activists from the Pacific region together to work on social reforms and to foster peace through international understanding and acceptance.

[30] The following year, she attended the 1938 World Youth Congress, held at Vassar College in Poughkeepsie, New York, and was featured on the front page of the Honolulu Advertiser with Chinese student Pearl Teh-Wei Liu of Hong Kong as symbols of peace, in spite of their countries' ongoing war.

[31] After graduating in 1939, Matsuoka made her way home to Japan, after stopping in Amsterdam to attend the World Christian Youth Conference as a delegate of the Tokyo YWCA and touring Europe.

[36] The changes the war brought were already visible as she sailed through the British ports at Colombo (now in Sri Lanka), Singapore, and Hong Kong, before arriving in Shanghai,[37] where she witnessed the aggressive treatment towards Chinese people by the Japanese military.

[41] After her return, Matsuoka consulted with Count Aisuke Kabayama about finding a job that would allow her to promote world peace and international understanding.

[46] Shortly after the wedding, Japan declared war upon the United States and Matsuoka resigned herself to hoping that after the conflict positive relationships could be restored.

[51] Matsuoka, her mother, her sister Reiko, and daughter Seiko fled the bombings in Tokyo and spent the months prior to the surrender of Japan in Hanamaki.

When offered a job at the Reader's Digest in November, Matsuoka began working at the Japanese editorial office, spending much of her time serving as an interpreter for foreign correspondents.

[56][57][58] She also worked with Laura Lou Brookman, managing editor of the Ladies' Home Journal[59][60] and Keyes Beech, a Pulitzer Prize-winning journalist who focused on Asia.

[57][58][60] Initially, Matsuoka was happy with the reforms brought about by the American administrators,[61] and even took her daughter with her to vote when women's suffrage was granted in 1946.

[69] She began to write articles for various magazines and newspapers,[70] providing social criticism of government policies, which had shifted from reforming and democratizing Japan to reconstructing the economy and re-militarizing the country to be an ally to the West during the Cold War.

[72] Matsuoka was hired by John Hersey as his agent and translator for Hiroshima, but because of the war department censorship was unable to get permission for publication of her version.

Reviewers praised the work, which according to Thomas M. Curran of America, a national Catholic weekly magazine, was a "sensitive study of the 'Oriental Mind'" and critically evaluated Japanese values in the pre- and post-war periods.

[88] William Heinemann wrote in The Adelaide Advertiser that Matsuoka's broad cultural experiences allowed her to contrast Western and Eastern thoughts on the war and occupation bringing insights to readers.

[96] Matsuoko was strongly opposed to the Republic of Korea–Japan Talks,[97] a US-backed series of negotiations that took place between 1951 and 1965 to enact a treaty normalizing the relationship between the two countries.

[100] Matsuoko and Kenzo Nakajima, another writer, led an intellectual organization, Ampo Hihan no Kai (The Association for Criticizing the Security Treaty), founded in 1959.

[104] In the wake of large scale demonstrations, the treaty was revised in 1960 to create more mutuality for Japan's defense and collaboration on the mobilization of military forces.

[105][106] Matsuoka gained a reputation as a critic of imperialist and militaristic policies,[107][108] and in the 1960s the view that she was anti-American began limiting publication of her articles.

She saw expansion of the Soviet Union across Eastern Europe, as well as its occupation of northern Japanese islands and patrols with warships in the Indian Ocean, as imperialistic and militaristic actions.

[121][122] In 1970, Matsuoka and Aiko Iijima [fr; ja] decided to host a conference to demonstrate their disagreement with Japanese aggression towards other Asians.

[123] A critical component of the movement in Japan, as opposed to anti-discrimination and equality aims in the United States, was examination of how Asian people fought against imperialism and oppression and how women could create strategies to improve power imbalances.

[107][126] She denounced expansion of hostilities into Cambodia and Laos in 1971, noting that the spread of aggression was impacting the traditional unity of the Indochinese people.

She criticized the governments of both Japan and the US for on-going militaristic policies in Asia[127] and continued to fight for a treaty to foster peace and friendship with China,[128] which was finally ratified in 1978.