Levinthal was a founder of the Orthodox Union in 1898 and of Mizrachi (now Religious Zionists of America) in 1902; he was present at the 1906 founding of the American Jewish Committee as a delegate, and helped organize the American Jewish Congress in 1917. In 1919, he was sent by the American Jewish Committee to the Peace Conference at Versailles, one of only nine Jewish representatives. While there, he advocated for successful resolutions supporting religious freedom and Jewish civil rights of Jews in Europe.