mcadoo was born in ramelton, county donegal, ireland on october 25, 1853. he immigrated to the united states with his parents, who settled in jersey city, new jersey, in 1865, where he attended public school. he studied law, was admitted to the bar in 1874 and commenced practice in jersey city. he was employed as a newspaper reporter from 1870 to 1875. he was a member of the new jersey general assembly in 1882.