Ira Allen was born in Cornwall, Connecticut, the youngest of six sons born to Joseph and Mary (Baker) Allen. In 1771 Allen went to Vermont as surveyor for the Onion River Land Company. The Allen brothers established the company in order to purchase lands under the New Hampshire Grants. Through this Allen was involved in a dispute with New York over conflicting land claims in the region.
He was a member of the Vermont Legislature, in 1776–1777, and was a leading figure in the declaration of the Vermont Republic in 1777. He and his brother Ethan, along with Thomas Chittenden and others, were implicated in potentially treasonous actions when they entered into negotiations with Frederick Haldimand that suggested they might turn Vermont over to the British. An alternate explanation is that they used the Haldimand negotiations to both stave off a British invasion of Vermont from Canada, and to prod the Continental Congress into recognizing Vermont as an entity separate from New York and New Hampshire and admitting it to the United States.
In 1780 he presented to the Legislature a memorial for the establishment of the University of Vermont. He contributed money and a fifty-acre (20 ha) site at Burlington. He was called the "Metternich of Vermont" and the "Father of the University of Vermont." Ira Allen pledged 4000 British pounds sterling to the University of Vermont, but never donated that money. In response, the Trustees of the University of Vermont secured a Writ of Attachment on his title to the town of Plainfield to try to extract payment of his original 4000 pound pledge.
In 1789 he married Jerusha Enos, the daughter of Roger Enos and Jerusha Hayden Enos. Members of the Allen and Enos families were the original proprietors of Irasburg. Ira Allen subsequently acquired all the proprietary rights to Irasburg, and deeded the town to Jerusha Enos as a wedding gift.
He went to France in 1795, and sought French army intervention for seizing Canada, to create an independent republic called United Columbia. He bought 20,000 muskets and 24 cannon, but was captured at sea, taken to England, placed on trial, charged with furnishing arms for Irish rebels, but was acquitted after a lawsuit which lasted eight years.
He died in Philadelphia, where he had gone to escape imprisonment for debt. He was originally buried in Philadelphia's Arch Street Presbyterian Cemetery, but his remains were lost when that site was destroyed. There is a cenotaph in his memory at Wetherills Cemetery in Audubon, Pennsylvania, and another at Greenmount Cemetery in Burlington, Vermont.
He published books:
- The Natural and Political History of Vermont. London: J.W. Myers. 1798. ISBN 0-8048-0419-2.
- Statements Appended to the Olive Branch, (1807)
- "Ira Allen (1751–1814)". Virtual Vermont. 2010. Retrieved 2010-03-09.
- A.J.H Dyer (1896). "General Ira Allan". The American Monthly Magazine, Daughters of the American Revolution (R.R. Bowker Co.): 61.
- John Howard Brown (1900). Lamb's biographical dictionary of the United States. James H. Lamb Co. pp. 66–67.
- Graffagino, J. Kevin (1991). "A Hard Founding Father to Love". In Daniels, Robert. The University of Vermont, The First Two Hundred Years. Hanover NH: University of Vermont, distributed by University Press of New England. ISBN 0874515491.
- Vermont Secretary of State, Legislative Directory, 1981, page 105
- William W. Stickney (1901). "Farewell address of William W. Stickney". Vermont Journal of the Joint Assembly (Montpelier, VT: Vermont State Archives and Records Administration): 14.
- Vermont Historical Society Collections. Montpelier: Vermont Historical Society. 1871. p. 427.
- Vermont Development Commission, Vermont Life magazine, Volumes 41–42, 1986, page 45
- Hamilton Child, Gazetteer and Business Directory of Lamoille and Orleans Counties, Vt., 1883, page 288
- Ethan Allen, Ethan Allen and His Kin: Correspondence, 1772–1819, Volume 1, 1998, page 334
- Robert E. May (2002). Manifest Destiny's Underworld: Filibustering in Antebellum America. U. of North Carolina Press. ISBN 0-8078-2703-7. Retrieved 23 July 2008. Chapter 1
- Benson John Lossing (1851). The pictorial field-book of the revolution. Harper & Bros. p. 161. ISBN 0-87152-056-7.
- Ethan Allen Hitchcock, William Augustus Croffut (1909). Fifty years in camp and field: diary of Major-General Ethan Allen Hitchcock, U.S.A.. G.P. Putnam's Sons. p. 31.
- Vermont Historical Society Collections I. Montpelier: Vermont Historical Society. 1870.
- Vermont Historical Society Collections II. Montpelier: Vermont Historical Society. 1871.
- Inventory of the Allen Family Papers, Special Collections, University of Vermont Library