Born in Kanagawa Prefecture, he converted to socialism in 1904 while working at the Yokosuka Naval Arsenal, where he read anti-war pamphlets by Kōtoku Shūsui, Sakai Toshihiko, and other socialists.

After the Russo-Japanese War, Arahata wrote for numerous socialist publications; his account of the Ashio Copper Mine incident is considered a classic of Japanese journalism.

[1] After World War II, he served on numerous labor committees, and was elected the first chairman of the National Trade Union of Metal and Engineering Workers.

He also helped found the Japan Socialist Party in 1945, joining its Central Committee in 1947 and winning elections to the National Diet on its slate in 1946 and 1947.

In 1948, Arahata's opposition to the party's approval of postal, tobacco tax, and train fare increases led him to leave its ranks.