John Mitchel was born in Fordham, New York in 1879. The grandson of John Mitchel, the Irish nationalist leader who emigrated to the United States in 1853.
Mitchel became a lawyer and in 1906 took part in an investigation of corrupt New York City officials. In 1913 he was elected as the youngest mayor in the city's history. He introduced a number of civic reforms including a program of tax relief. However, he was removed from power in 1917 by Charles Murphy and the powerful Tammany Society.