Josiah Cohen was born in Plymouth, England, to a Jewish family long settled in Cornwall, and immigrated to the United States in 1857.

In 1860 he entered upon the duties of teacher in the school of the Rodef Shalom Congregation in Pittsburgh, and continued that vocation until 1866, when he was admitted to the bar of Allegheny County.

[4] He was chairman of the Allegheny County Republican executive committee, and, in 1884, one of the members of the presidential election board for Pennsylvania.

Cohen was affiliated with most of the local and national Jewish organizations, being a founder and member of the executive committee of the Union of American Hebrew Congregations, and president of District Lodge No.

At the time of his death in 1930 he was the second oldest active jurist in the country, after Oliver Wendell Holmes.