Nugent was born in County Galway but travelled with his parents to the United States at an early age.
In 1848, Nugent was leaked a copy of the Treaty of Guadalupe Hidalgo, which would end the Mexican–American War after it was amended and approved by the Senate.
In 1856 he opposed the re-establishment of the San Francisco Committee of Vigilance, an extra-legal organization for the preservation of law and order.
In 1858, President James Buchanan appointed Nugent special agent to New Caledonia (British Columbia).
Buchanan wanted to see how Americans and their interests were faring in the area in light of the Fraser Canyon Gold Rush.
Nugent appears to have created a rift through a dispute with Governor James Douglas over the treatment of American citizens in the courts.