[1] Born in Hayashida village, Okayama prefecture (present-day Tsuyama city), Ōta graduated from the Department of Applied Chemistry of Osaka Imperial University.

In 1950, Ōta helped establish the Japanese Federation of Synthetic Chemistry Workers' Unions (Gōka Rōren) as an affiliate of Sōhyō, and would remain chairman of its central committee until 1979.

[2] The following year, three of Sōhyō's largest unions bolted to form the more moderate, openly anti-communist Zenrō labor federation, precipitating the ouster of Takano.

As leader of Sōhyō, Ōta adhered to Takano’s vision of a wide-ranging political activism, but sought to steer clear of the increasingly unpopular Japan Communist Party and more directly address workers' immediate economic concerns.

This made any particular union reluctant to strike for higher wages and better working conditions, for fear that rival companies would simply snap up market share during the stoppage.

[6] Ōta presided over the Japanese labor movement at the height of its postwar power, demonstrating Sōhyō's organizational strength by carrying out some of the largest strikes in Japan's history in support of the 1960 Anpo protests against the U.S.-Japan Security Treaty.

[5] At the same time, Ōta was also overseeing Sōhyō's efforts on behalf of one of its member unions in the massive 1960 Mitsui Miike Coal Mine Strike, which ultimately grew to become the largest militant conflict between management and labor in Japan's modern history.