Donnelly was the son of Philip Carrol Donnelly, an Irish Catholic immigrant who had settled in Philadelphia, Pennsylvania. His sister was the writer Eleanor C. Donnelly. On June 29, 1826, Philip had married Catherine Gavin, a

Donnelly entered politics, this time as a Republican, with two unsuccessful campaigns for the state legislature (1857, 1858). Though he was not

Donnelly's writings on Atlantis have been rejected by scholars and scientists. He has been described as a crank and pseudoscience promoter.
Gordon Stein has

• Bovee, John (1969). 'Doctor Huguet: Donnelly on Being Black', Minnesota History, vol. 41 (no. 6), pp. 286–94.
• William Friedman

During the 1930s, an organization was formed to lobby for the creation of a state park at Donnelly's home at Nininger near Hastings, Minnesota. The house was still standing in 1939, but the

His books include:
• The Mourner's Vision: A Poem (1850), a long poem he wrote at the age of 18.
• Atlantis: The Antediluvian World (1882), in which he attempted to