Crosby was born in Harwich, Massachusetts on January 4, 1750, the son of Thomas and Elizabeth Crosby. His family moved to what is now Putnam County, New York when Crosby was only an infant. The family was poor, and by 1766, Crosby set out from home to find a career. He became an apprentice shoemaker in Kent, New York, and continued in the apprenticeship until it was completed in 1771 on his 21st birthday. When the Revolutionary War began, he was in Danbury, Connecticut, and he immediately enlisted as a soldier.
Crosby enlisted with a Connecticut regiment in the first weeks of the war. His unit became part of the invasion of Canada by the Continental Army in 1775. Following the capture of Montreal, his enlistment expired and he returned to Danbury to continue his career as a shoemaker.
At this time, nearby Westchester County, New York was a 'neutral ground' between the British forces controlling New York City in the south and colonial forces in the north. In addition to regular armies, the county was host to vigilante gangs that claimed to support each side in the conflict in order to justify pillage.
By September, 1776, Crosby had left behind his shoemaking to return to the Continental Army, and made his way to the camp at White Plains in Westchester County. On the way, as a result of misunderstanding, Crosby was invited to join a meeting of loyalist locals who were intending to support the British efforts in the area. He was able to deliver the information he learned to John Jay, a member of the local Committee of Safety, and at Jay and Crosby's direction the group of loyalists was arrested.
He was recruited to spy full-time by Jay, and in order to gain entry into loyalist and British circles he adopted the identity of a spy employed by the British General Howe. By doing this, he became an object of hatred for many of his friends and family. Crosby requested that if he died, the Committee of Safety would clear his name of supporting the British, and they also gave him a special pass to be used in an emergency if he was captured by American forces.
Crosby served as a spy in Westchester County, further north near Lake Champlain, and in other areas. He followed the same pattern of infiltration, capture, and escape at least four times. The intelligence he provided was used both to capture loyalists and undermine local support for the British, and on at least one occasion proved useful to the Commander of the Continental Army, George Washington. He was repeatedly captured by Americans who believed him to be a loyalist, and consequently repeatedly escaped.
Following the War, Crosby and his brother purchased a farm, and he lived on that land until his death.
As reported in his obituary in the Cabinet Newspaper (Schenectady, NY), July 8, 1835, p. 3, Crosby's life was the basis for the character Harvey Birch in The Spy, a novel published in 1821 and authored by the American writer James Fenimore Cooper. Cooper may have heard of Crosby's story from John Jay, although Jay apparently did not reveal Crosby's name, fearing retribution from the spy's enemies.
- Intelligence in the American Revolutionary War
- Intelligence operations in the American Revolutionary War
- Bailey, James Montgomery; Bailey, Jame Montgomery and Hill, Susan Benedict (1896). History of Danbury, Connecticut, 1684-1896. p. 103.
- Miller, Harry Edward (1898). "The Spy on Neutral Ground". The New England Magazine (The New England Magazine Company) 18. Retrieved 2009-06-24.
- "Intelligence Operations". Intelligence in the War of Independence. Central Intelligence Agency Center for the Study of Intelligence. Retrieved 2009-06-24.
- Rintoul, M.C. (1993). Dictionary of real people and places in fiction. Taylor & Francis. p. 337. ISBN 978-0-415-05999-2.