Markoe was born in St. Croix, in what was then the Danish West Indies. His grandfather, Pierre Marcou, a French Huguenot, had left France for the Danish West Indies before the revocation of the Edict of Nantes. His father was Pierre Markoe, who changed the family name to Markoe, and married Elizabeth Farrell.
In St. Croix, Markoe became rich by inheritance and trading with both American colonies and Europe. He married a widow, Elizabeth (Kenny) Rogers, in 1751, and had two sons, Peter and Abraham, Jr.
When there were indications of rebellion, Markoe was the founder and the first Captain of the Philadelphia Light Horse, known today as the First Troop Philadelphia City Cavalry. The unit was composed of rich gentlemen of the city, who paid for their own horses and equipment. When the Continental Congress appointed George Washington the Commander in Chief, and Washington departed for Massachusetts on June 21, 1775, the Philadelphia Light Horse escorted him through New Jersey to New York City.
As a Danish subject, Markoe could not actually fight in the war because of the King of Denmark's Neutrality Edict, but he did contribute to the American war effort in many other ways. One early contribution was a regimental flag with thirteen stripes representing the thirteen colonies that were striving to become the original thirteen states.
- "MARKOE, ABRAHAM". Digitization for Access and Preservation. University of the Virgin Islands Libraries and the Virgin Islands Division of Libraries, Archives, and Museums. 1999-2000. Retrieved 2010-08-31. "July 2, 1727 – August 28, 1806 Abraham Markoe, Capitalist, Patriot was born in Santa Crux, (St. Croix) the then Danish West Indies."
- Alotta, Robert (1990). Mermaids, Monasteries, Cherokees, and Custer. Chicago: Bonus Books. p. 151. ISBN 0-933893-90-6.
- "Collection 1935:Markoe family Papers, 1773–1940". Historical Society of Pennsylvania (Abstract). Retrieved 2010-09-02. "Abraham Markoe ... moved to Philadelphia ca. 1770. He left his son, Abraham Markoe, Jr., behind to manage the sugar plantations."
- "History:Philadelphia (1774–1775)". FTPCC web site. First Troop, Philadelphia City Cavalry. Archived from the original on 18 August 2010. Retrieved 2010-09-01. "Abraham Markoe, a Danish subject, was chosen to be the first Captain because of his energy in organizing the Troop and his previous Danish military experience. Though prevented from open participation in the War as a result of the Neutrality Edict issued by then King Christian VII of Denmark, Captain Markoe took an active part in the defeat of the enemy by all other available means."
- Johnson, Robert (2006). Saint Croix 1770–1776: The First Salute to the Stars and Stripes. AuthorHouse. p. 20. ISBN 978-1-4259-7008-6. "This same Abraham Markoe, in 1775, organized the Light Horse Troop of Philadelphia, and presented the troop with what is considered the first flag with thirteen stripes representing the thirteen colonies."
- The Markoe Family papers, containing various family correspondences, are available for research use at the Historical Society of Pennsylvania.
- Abraham Markoe at Find a Grave